Acoustic condition sensor employing a plurality of mutually non-orthogonal waves

ABSTRACT

A touch sensor comprising an acoustic wave transmissive medium having a surface; a plurality of acoustic wave path forming systems, each generating a set of incrementally varying paths through said transmissive medium; and a receiver, receiving signals representing said sets of waves, a portion of each set overlapping temporally or physically by propagating in said transmissive medium along axes which are not orthogonal. The waves may also be of differing wave modes. The receiver system may include a phase, waveform or amplitude sensitive system. Reflective arrays are associated with said medium situated along a path, said path not being a linear segment parallel to a coordinate axis of a substrate in a Cartesian space, a segment parallel to an axial axis or perpendicular to a radial axis of a substrate in a cylindrical space nor parallel and adjacent to a side of a rectangular region of a small solid angle section of a sphere; situated along a path substantially not corresponding to a desired coordinate axis of a touch position output signal; situated along a path substantially non-parallel to an edge of said medium; has a spacing of elements in said array which differs, over at least one portion thereof, from an integral multiple of a wavelength of an incident acoustic wave; has elements in said array which are non-parallel; has an angle of acceptance of acoustic waves which varies over regions of said array; and/or coherently scatter at least two distinguishable acoustic waves which are received by said receiving system.

CONTINUING DATA

[0001] The present application for U.S. patent is a Continuation-in-Partof U.S. patent application Ser. No. 08/424,216, allowed, expresslyincorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates to an acoustic touch positionsensor, and more particularly to such a sensor wherein a coordinateposition, and optionally an absorption characteristic, of an acousticdisturbance is determined by analyzing a plurality of received signals.The present invention allows the sensing system to employ waves todiffer in path geometry, and/or wave characteristic type, e.g., mode,frequency, waveform, velocity, and/or wavelength. This systemadvantageously allows redundant position measurement and/or differentialwave perturbation sensing.

BACKGROUND OF THE INVENTION

[0003] Acoustic touch position sensors are well known. A common systemincludes two sets of transducers, each set having a different axisaligned respectively with the axes of a physical Cartesian coordinatesystem defined by a substrate. An acoustic pulse is generated by onetransducer, propagating as a Rayleigh wave along an axis whichintersects an array of reflective elements, each element angled at 45°and spaced corresponding to an integral number of wavelengths of theacoustic wave pulse. Each reflective element reflects a portion of thewave along a path perpendicular to the axis, across an active region ofthe substrate, to an opposing array and transducer which is a mirrorimage of the first array and transducer. The transducer in the mirrorimage array receives an acoustic wave consisting of superposed portionsof the wave reflected by the reflective elements of both arrays,directed antiparallel to the emitted pulse. Wavepaths in the activeregion of the sensor have characteristic time delays, and therefore awavepath or wavepaths attenuated by an object touching the active regionmay be identified by determining a timing of an attenuation in thecomposite returning waveform. A second set of arrays and transducers areprovided at right angles to the first, and operate similarly. Since theaxis of a transducer corresponds to a physical coordinate axis of thesubstrate, the timing of an attenuation in the returning wave isindicative of a Cartesian coordinate of a position on the substrate, andthe coordinates are determined sequentially to determine the twodimensional Cartesian coordinate position of the attenuating object.

[0004] The applicability of such systems as commonly employed isrestricted by the following major limitations. First, acousticallyabsorptive contamination in localized regions, e.g. a water drop on aknown Rayleigh-wave sensor, result in large areas of shadowing in whichtwo-dimensional touch positions cannot be reconstructed. Second, theconfigurational requirements of these sensors limits their versatilitywith regard to shape and size. Third, reconstruction of touchcoordinates may lead to ambiguities when more than one touch is appliedsimultaneously. Finally, such sensors provide limited touchcharacteristic information from which to differentiate valid touchesfrom false touches, e.g. fingers from water drops. The present inventionaddresses these problems.

[0005] Present commercial touch screen products generally serveapplications in which the touchscreen is an input device that isintended to be used by one user at a time. An automatic-teller-machine(ATM) banking application is typical. While many customers maysequentially use a touchscreen based automatic teller machine, each userin turn has a private dialog with the system. In contrast, few if anytouchscreen products are presently available for applications in whichthe touchscreen is an input device that is intended to be used by morethan one user simultaneously.

[0006] a. Parallel Transducer Arrays

[0007] Acoustic touch position sensors are known to include a touchpanel or plate having an array of transmitters positioned along a firstedge of a substrate for simultaneously generating parallel surfaceacoustic waves that directionally propagate through the panel to acorresponding array of detectors positioned opposite the first array ona second edge of the substrate. Another pair of transducer arrays isprovided at right angles to the first set. Touching the panel at a pointcauses an attenuation of the waves passing through the point of touch,thus allowing interpretation of an output from the two sets oftransducer arrays to indicate the coordinates of the touch. This type ofacoustic touch position sensor is shown in U.S. Pat. No. 3,673,327 andWO 94/02911, Toda, incorporated herein by reference. By employing adirect acoustic path from a transmitting transducer to a correspondingreceiving transducer, an acoustic path length which is approximatelyequal to the height or width of the substrate is provided, as shown inFIG. 1. Because the acoustic wave diverges, a portion of a wave emittedfrom one transmitting transducer will be incident on a set of receivingtransducers, as shown in FIG. 2.

[0008] b. Reflective Arrays

[0009] In order to reduce the number of transducers required for anacoustic touchscreen, Adler, Re. 33,151, and U.S. Pat. No. 4,700,176,provide a reflective array for reflecting portions of an acoustic wavealong incrementally varying paths. Therefore, if two such arrays aredisposed opposite one another, as shown in FIG. 4, a single transmit andreceive transducer will allow touch sensing along one axis of thesubstrate, with a maximum acoustic path length of twice the height pluswidth or twice the width plus height of the touch sensitive area. Themaximum acoustic path length is a useful metric for acoustic touchsensors because most materials, e.g., glass, have a relatively constantacoustic power loss expressed in dB per unit length; the greater thepath length, the greater the attenuation. In many cases, it is thisattenuation of the acoustic signal which limits the design of thetouchscreen, and therefore it is generally desired to have high acousticefficiency in each of the touchscreen components to allow design leeway.Thus, for example, greater numbers of transducers may be selectivelydeployed to allow larger substrates, and likewise, with limited sizesubstrates, acoustic paths may be folded to reduce a required number oftransducers.

[0010] In order to provide a set of surface acoustic waves whichpropagate across a broad region of the substrate in parallel, anacoustically reflective grating having elements set at 45° to the axisof the beam is disposed along its path, each element reflecting portionsof the wave at right angles to the axis of propagation. The acousticwaves are then collected, while maintaining the time dispersioninformation which characterizes the axial position from which anattenuated wave originated. The position of a touch in the active areais thus determined by, e.g., providing another reflective gratingopposite the first, which directs the surface acoustic waves as asuperposed wave to another transducer along an antiparallel path,recording the time of arrival and amplitude of a wave pattern, anattenuation of which corresponds to a touch and a characteristic timecorresponding to a position along the axis of the arrays. The touch, inthis case, may include a finger or stylus pressing against the surfacedirectly or indirectly through a cover sheet. See, e.g., U.S. Pat. No.5,451,723. In addition, if the emitted wave diverges, one of thereflective arrays may be eliminated, as shown in FIG. 3, although arectangular coordinate system is not provided. In the case shown in FIG.3, the maximum path length is approximately the height plus the width.Acoustic touch position sensors are also known wherein a singletransducer per axis is provided for emitting a surface acoustic wave, asshown in FIG. 5. In this case, the maximum path length is two times thesum of the height plus width.

[0011] The known reflective arrays are generally formed of a glass fritwhich is silk-screened onto a soda-lime glass sheet formed by a floatprocess, and cured in an oven to form a chevron pattern of raised glassinterruptions. These interruptions typically have heights or depths oforder 1% of the acoustic wavelength, and therefore only partiallyreflect the acoustic energy.

[0012] Thus, with waves having surface energy, the reflecting arrays maybe formed on the surface, and where wave energy is present on both sidesof the substrate, these reflecting arrays may be formed on one or bothsides of the substrate. Because the touch sensor is generally placed infront of a display device, and because the reflective array is generallyoptically visible, the reflective arrays are generally placed at theperiphery of the substrate, outside of the active sensing area, and arehidden and protected under a bezel. The reflective elements of thereflective array each generally reflect of order 1% of the surfaceacoustic wave power, dissipating a small amount and allowing theremainder to pass along the axis of the array. Thus, array elementscloser to the transmitting transducer will be subject to greaterincident acoustic energy and will therefore reflect a greater amount ofacoustic power. In order to provide equalized acoustic power at thereceiving transducer, the spacing of the reflective elements may bedecreased with increasing distance from the transmitting transducer, orthe acoustic reflectivity of the reflective elements may be altered,allowing increased reflectivity with increasing distance from thetransmitting transducer.

[0013] Adler, US Re. 33,151, relates to a touch-sensitive system fordetermining a position of a touch along an axis on a surface. A surfaceacoustic wave generator is coupled to a sheet-like substrate to generatea burst of waves, which are deflected into an active region of thesystem by an array of wave redirecting gratings. According to adisclosed example, surface acoustic waves traversing the active regionare, in turn, redirected along an axis by gratings to a receivingtransducer. A location of touch is determined by analyzing a selectiveattenuation of the received waveform in the time domain, eachcharacteristic delay corresponding to a locus on the surface. Theredirecting gratings are oriented at 45° to the axis of propagation, andspaced at integral multiples of the surface acoustic wave wavelength,with dropped elements to produce an approximately constant surfaceacoustic wave power density over the active area. The spacing betweengrates decreases with increasing distance along the axis of propagationfrom the transducer, with a minimum spacing of at least one wavelengthof the transmitted wave. U.S. Pat. Nos. 5,329,070, 5,260,521, 5,234,148,5,177,327, 5,162,618 and 5,072,427 propose specific examples of types ofsurface acoustic waves that may be used in the acoustic sensor systemtaught in the Adler patents.

[0014] Where a separate reflective array is provided to redirectacoustic waves toward the receiving transducer, these are also providedwith an increasing acoustic reflectivity with increasing distance fromthe receiving transducer. This is to reduce signal loss with propagationof the signal toward the receiving transducer along the axis of thereflective array. Typically, array pairs are designed as mirror imagesof one another.

[0015] U.S. Pat. No. 4,642,423, to Adler, incorporated herein byreference, addresses pseudo-planarization techniques for rectangulartouchscreen surfaces formed by small solid angle sections of a sphere.According to Adler, reflective elements are angled to excite waves alongsections of great circles of the spherical surface which extrapolate toa common intersection point. This patent addresses the need fortouchscreens that match the curvature of CRT faceplates, for which theradius of curvature is always large compared to the diagonal dimensionof the faceplate. This patent teaches means to minimize the inherentdifferences between spherical geometry of a small portion of a sphereand the Cartesian plane, allowing use in conjunction with controllersthat are designed for flat sensor geometry. The acoustic waves generatedby the system of Adler are substantially orthogonal. Known embodimentsof the Adler technology include 19 inch diagonal CRTs with a radius ofcurvature of 32 inches and 13 or 14 inch diagonal CRTs with a radius ofcurvature of 22.6 inches.

[0016] c. Two Dimensional Position Sensing

[0017] In order to receive information determinative of the coordinatesof a touch, two acoustic waves, each propagating across the activeregion of the substrate along perpendicular axes are provided. Thus, thetwo axes are typically used in conjunction to recognize a valid touch,but may also be analyzed separately and non-interactively tosequentially determine a position along each of the two orthogonalcoordinate axes. In these known systems, the coordinate axes of interestto the application are defined by the physical configuration of thesensor. Thus, sensor design is constrained by the requirements of theapplication's coordinate system.

[0018] In known systems, the system operates on the principle that atouch on the surface attenuates surface acoustic waves having a powerdensity at the surface. An attenuation of a wave traveling across thesubstrate causes a corresponding attenuation of waves impinging on thereceive transducer at a characteristic time period. Thus, the controllerneed only detect the temporal characteristics of an attenuation todetermine the axial coordinate position. Measurements are taken alongtwo axes sequentially in order to determine a Cartesian coordinateposition.

[0019] Other known systems, described in more detail below, employ asingle reflective array for separating as a plurality of wave paths, andsuperposing as a composite waveform, the signal from the transducer,through the active region, along a plurality of paths and then back tothe transducer, by providing an acoustically reflective edge spacedparallel to the reflective array, causing the dispersed wave to traversethe active region twice, as shown in FIG. 5. See, U.S. Pat. No.5,177,327, FIG. 10 and accompanying text, incorporated herein byreference.

[0020] FIG. 11 of U.S. Pat. No. 4,700,176 teaches the use of a singletransducer for both transmitting the wave and receiving the sensingwave, with a single reflective array employed to disperse and recombinethe wave. Such systems therefore employ a reflective structure oppositethe reflective array. As a result, an acoustic wave passes through theactive region twice, with consequent increased wave absorption by thetouch but also increased overall signal attenuation due to thereflection and additional pass through the active region of thesubstrate. Thus, the acoustic wave may be reflected off an edge of thesubstrate or an array of 180° reflectors parallel to the axis of thetransmission reflective grating and reflected back through the substrateto the reflective array and retrace its path back to the transducer. Thetransducer, in this case, is time division multiplexed to act astransmitter and receiver, respectively, at appropriate time periods. Asecond transducer, reflective array and reflective edge are provided foran axis at right angles to allow determination of a coordinate of touchalong perpendicular axes.

[0021] A known system by Electro-Plasma (Milbury Ohio) employs abisected reflecting array in order to reduce an acoustic wavepath, asshown in FIG. 6A. Therefore, a maximum path length of an acoustic wavealong the composite reflecting array from a transducer is about one halfof the total width, with transducers each sending acoustic waves towardthe bisection point. Thus, the orthogonal set of paths will be longer,with a maximum total path length of two times the height plus the width.In this system, transmitting transducers are excited individually andproduce identical types of waves, portions of which travel alongparallel paths, with a small overlap of acoustic wave coverage of thetouchscreen in order to avoid a dead zone in the touch region. Theacoustic waves follow the traditional paths corresponding to axesparallel to the Cartesian coordinate axes. A similar type system wouldbisect both sets of reflective arrays, as shown in FIG. 6B.

[0022] The “triple transit” system, shown in FIG. 8, provides for asingle transducer which produces a sensing wave for detecting touch ontwo orthogonal axes, which both produces and receives the wave from bothaxes. In this case, the area in which touch is to be sensed is generallyoblong, such that the longest characteristic delay along one path isshorter than the shortest characteristic delay along the second path,thereby allowing differentiation between the two axes based on time ofreception. See, U.S. Pat. Nos. 5,072,427, 5,162,618, and 5,177,327,incorporated herein by reference. The maximum path length of the tripletransit design is four times the width plus two times the height. Due tothe significant difference in path lengths, the X and Y signals arenon-overlapping, as shown in FIG. 9C.

[0023] d. Controller Algorithms

[0024] The wave pattern of one type of known acoustic touch sensors isdispersed along the axis of the transmitting reflective array, traversesthe substrate and is recombined, e.g., by another reflective grating,into an axially propagating wave, dispersed in time according to thepath taken across the substrate, and is directed to a receivingtransducer in a direction antiparallel to the transmitted wave, whichreceives the wave and converts it into an electrical signal forprocessing based on signal amplitude received as a function of time.Thus, according to this system, only two transducers per axis arerequired. Because of the antiparallel path, the time delay of aperturbation of the electrical signal corresponds to a distance traveledby the wave, which in turn is related to the axial distance from thetransducer along the reflecting arrays traveled by the wave beforeentering the active area of the substrate, i.e., approximately two timesthe distance along the axis of the array plus the spacing between thearrays. A typical set of return waveforms is shown in FIG. 9.

[0025] The location of a touch is determined by detecting an attenuationof the received signal amplitude either in absolute terms or as comparedto a standard or reference received waveform. Thus, for each axis, adistance may be determined, and with two orthogonal axes, a uniquecoordinate for the attenuation determined. Acoustic touch positionsensors of this type are shown in U.S. Pat. Nos. 4,642,423, 4,644,100,4,645,870, 4,700,176, 4,746,914 and 4,791,416, incorporated herein byreference. U.S. Pat. Nos. Re. 33,151, and 4,700,176 also disclose atouch sensor system having a set of diverging acoustic paths which areincident on a reflective array having elements located along an arc andspaced to meet coherency criteria. See, Re. 33,151. and 4,700,176, FIG.16 and accompanying text, incorporated herein by reference. This touchsensor produces a unidimensional output which corresponds to an angularposition of a touch.

[0026] According to known systems, a number of algorithms are employedto determine the coordinate position of a touch. The simplest algorithmis a threshold detection, in which an amplitude of a received signal iscompared to a set value. Any dip below that value is consideredindicative of a touch. More sophisticated is an adaptive threshold, inwhich the threshold varies based on actual sets of received data, thusallowing increased sensitivity and rejection of artifacts of limitedamplitude.

[0027] A control circuit may operate in a number of modes, e.g., numberof transducers and configuration. In known systems having a rectangularsubstrate without redundancy, the number of transducers varies: 1(triple transit); 2 (ExZec/Carroll Touch); 4 (Adler); and 6(ElectroPlasma). There is a natural 8 transducer arrangement, notpresent in prior art designs, which is an extension of 6 transducerscheme in which 4 transducers are used for both X and Y axismeasurements; see FIG. 6B.

[0028] Known systems also include an adaptive baseline, in which anamplitude of the normal received signal over time is stored, and thereceived signal is compared to a baseline having a characteristictimeframe. In this system, an artifact in one position does notnecessarily reduce sensitivity at another.

[0029] Brenner et al., U.S. Pat. No. 4,644,100 relates to a touchsensitive system employing surface acoustic waves, responsive to boththe location and magnitude of a perturbation of the surface acousticwaves. The system according to U.S. Pat. No. 4,644,100 is similar inexecution to the system according to US Re. 33,151, while determining anamplitude of a received wave and comparing it to a stored referenceprofile.

[0030] In order to reduce the number of transducers, the known “tripletransit” system reflects the acoustic signal so that a wave emitted by asingle transducer is dispersed as parallel waves along a first axis,then reflected at a right angle and dispersed as parallel waves along asecond axis. These waves are then reflected back to the arrays and thenback to the transducer, so that all the waves traveling along the firstaxis are received by the transducer prior to any waves traveling alongthe second axis, generally requiring an oblong substrate. The controllertherefore sets two non-overlapping time windows for the received signal,a first window for the first axis and a second window for the secondaxis. Therefore, each time window is analyzed conventionally, and thepair of Cartesian coordinates is resolved.

[0031] A system for sensing a force of a stylus against an acoustictouch-sensitive substrate is disclosed in U.S. Pat. No. 5,451,723,incorporated herein by reference. This system converts the point-contactof the rigid stylus portion into an area contact of an acousticallyabsorptive elastomer, placed between the stylus and the substrate.

[0032] e. Wave Modes

[0033] “Surface acoustic waves” (“SAW”), as used herein refers toacoustic waves for which a touch on the surface leads to a measurableattenuation of acoustic energy. Several examples of surface acousticwaves are known.

[0034] The vast majority of present commercial products are based onRayleigh waves. Rayleigh waves maintain a useful power density at thetouch surface due to the fact that they are bound to the touch surface.Mathematically, Rayleigh waves exist only in semi-infinite media. Inpractice it is sufficient for the substrate to be 3 or 4 wavelengths inthickness. In this case one has quasi-Rayleigh waves that are practicalequivalents to Rayleigh waves. In this context, it is understood thatRayleigh waves exist only in theory and therefore a reference theretoindicates a quasi-Rayleigh wave.

[0035] Like Rayleigh waves, Love waves are “surface-bound waves”.Particle motion is vertical and longitudinal for Rayleigh waves. Bothshear and pressure/tension stresses are associated with Rayleigh waves.In contrast, particle motion is horizontal, i.e. parallel to touchsurface, for Love waves. Only shear stress is associated with a Lovewave. Other surface-bound waves are known.

[0036] Another class of surface acoustic waves of possible interest inconnection with acoustic touchscreens are plate waves. Unlikesurface-bound waves, plate waves require the confining effects of boththe top and bottom surfaces of the substrate to maintain a useful powerdensity at the touch surface. Examples of plate waves include symmetricand anti-symmetric Lamb waves, zeroth order horizontally polarized shear(ZOHPS) waves, and higher order horizontally polarized shear (HOHPS)waves.

[0037] The choice of acoustic mode affects touch sensitivity, therelative touch sensitivity between water drops and finger touches, aswell as a number of sensor design details. However, the basic principlesof acoustic touchscreen operation are largely independent of the choiceof acoustic mode.

[0038] f. Optimization for Environmental Conditions

[0039] The exposed surface of a touchscreen is ordinarily glass. Whilecertain systems may include such additions, electrically conductivecoatings or cover sheets are not necessary. Therefore, acoustictouchscreens are particularly attractive for applications which dependon public access to a durable touch interface.

[0040] Semi-outdoor applications, e.g., ATMs, ticket booths, etc., areof particular interest. Typically in such applications, the touchscreenis protected from direct environmental precipitation contact by a boothor overhang. However, indirect water contact, due to user transfer orcondensation is possible. Thus, users coming out of the rain or snowwith wet clothes, gloves or umbrellas are likely to leave occasionaldrops of water on the touchscreen surface. Water droplets have a highabsorption of Rayleigh waves in known systems; thus, a drop of water inthe active region will shadow the acoustic paths intersecting that drop,preventing normal detection of a touch along those axes.

[0041] One approach to limit water contact with the touchscreen surfaceis to employ a cover sheet. See U.S. Pat. No. 5,451,723. However, acover sheet generally reduces the optical quality of the displayed imageseen through the resulting sensor and leads to a less durable exposedsurface. Another approach to reducing the effects of water droplets isto employ a wave mode which is less affected by the droplets, such as alow frequency Rayleigh wave, see U.S. Pat. No. 5,334,805, a Lamb wave,see U.S. Pat. Nos. 5,072,427 and 5,162,618, or a zero order horizontallypolarized shear wave, see U.S. Pat. No. 5,260,521. These waves, however,also have reduced sensitivity, resulting in either reduced touchsensitivity of the touch system, increased susceptibility toelectromagnetic interference, or more expensive controller circuitry.

[0042] In the case of Rayleigh waves, a lower frequency operationrequires a thicker substrate, e.g., 3 to 4 wavelengths of the wave, andwider reflective arrays and transducers. The increased bulk of a sensordesigned for low-frequency Rayleigh waves is typically a seriousmechanical design problem. In the case of Lamb waves, a thin substrateis required, e.g., about 1 mm at about 5 MHz. These thin substrates arefragile, and Lamb waves have energy on both top and bottom surfaces,making optical bonding problematic due to signal damping. In the case ofa ZOHPS wave, in contrast to a Rayleigh wave, the relative sensitivityis greater to a finger than to water droplets. Further, ZOHPS wavessupport limited options for optical bonding, such as RTVs (siliconerubbers) which do not support shear radiation damping.

[0043] Shear sensors have two disadvantages in cold climates. Inparticularly cold climates, it is important for touchscreens to sensetouches of fingers of gloved hands. Shear waves have reduced sensitivitycompared to Rayleigh waves thus making detection of gloved fingers moredifficult. Secondly, in such climates, drops of water may freeze to formsolid ice. While liquid water does not strongly couple to horizontallypolarized shear waves, ice does. Thus drops of water which freeze on thetouchscreen surface will cause shadowing or blinding.

[0044] There remains a need for a touch position sensor which operatesreliably in the increasingly rugged environments to which such devicesare deployed. There thus exists a need to supplement existingtechnologies in order to extend the applicability of acoustic touchsensor systems.

[0045] g. Size Constraints.

[0046] Acoustic sensors of the Adler type have been considered for usein electronic white boards; see FIG. 10 and associated text in E.P.Application 94119257.7, Seiko Epson. At present, no commercialelectronic whiteboard products are available based on acoustic sensorstechnology. In part, this is because of size limitations for knownacoustic technology.

SUMMARY OF THE INVENTION

[0047] The present invention derives from an understanding that acousticposition measurement technology suffers from various limitations, whichmay be addressed by implementing a system with various forms of partialredundancy in the sensing waves. Thus, for each coordinate axis of theoutput, a plurality of sets of waves are provided bearing informationabout the position of a single touch along that axis. Therefore, anylimitation in the ability of one set of waves to determine a touchposition may be supplemented by information derived from at least oneother set of waves. Because the redundancy may be partial, otherinformation may be derived from the available sets of waves as well,including a characteristic of a touch and information relating to aplurality of touches.

[0048] According to one set of schemes for producing partially redundantsets of waves, a plurality of sets of waves are provided, eachpropagating at a different angle with respect to the axis along which atouch position is to be sensed. Each of the waves should be able tosense position along a significant portion of the axis. Thus, atraditional type touch system provides two sets of waves which are eachparallel to an edge of a rectangular substrate and produce waves whichpropagate perpendicular to the edges. Thus, each set of waves isdedicated sensing a position along a particular axis. Likewise, a knownbisected reflective array scheme overlaps waves over an insignificantportion of the touch sensitive surface, and the waves generated are ofthe same frequency, mode, axis of propagation and therefore areessentially fully redundant and likely bear essentially the sameinformation.

[0049] The present invention also extends these same principles toencompass a number of other embodiments, including acoustic touchsystems in which the acoustic waves travel along paths which are neitherparallel nor perpendicular to an edge of a substrate or travel along apath which is neither parallel nor perpendicular to a reflective array.Thus, the present invention relaxes constraints imposed in prior touchposition sensors through an understanding that the geometry of the touchsensor substrate, reflective arrays or acoustic paths need not limit thecoordinate system represented in an output. Thus, the present inventionmay provide control systems which are capable of performing coordinatesystem transforms and higher levels of analysis of the informationcontained in the acoustic signals than prior systems.

[0050] In forming this understanding that a control need not be limitedto a conversion of a characteristic timing of a perturbation of anacoustic wave into a coordinate position along a single axis, thepossibility of non-Euclidean geometric shapes is developed. Thus, whilethe prior art teaches that acoustic touch sensing may be applied tospherical portions of CRT faceplates, the goal of the prior art was toprovide a system in which analysis of the received acoustic signals wereas if the substrate were planar. Therefore, those prior art systems weredeveloped to compensate for the spherical aberrations in the design andplacement of the reflective arrays. Likewise, a known prior art systememploys a diverging set of waves incident on a reflective array to sensea unidirectional angular measurement. In this case, a control treats theunidimensional angular measurement as a single coordinate axis withouttransformation.

[0051] The present invention provides touch system flexibility allowinganalysis of waves which propagate along non-orthogonal axes in the touchsensitive region of the touchscreen. Further, the present inventionprovides a touchscreen system which tolerates and analyzes waves whichare overlapping in time, i.e., simultaneously impinging on one or morereceiving transducers. Together, these related aspects of the inventionprovide greatly enhanced flexibility in the design of the touchscreen,with improved performance under adverse conditions.

[0052] The present invention also includes touch sensors for purposesother than graphic user interfaces. For example, applications in thefield of robotics exist, in which it is desirable to endow robots with asense of touch. While a number of sensor technologies exist, acousticsensing provides an opportunity for a large area, high resolution, lowcost per unit area sensor on a machine, for example, to detect contactor pressure with an adjacent object and to determine the location of thetouch. Such machines often have nonplanar surfaces, and as such it isadvantageous to provide a touch position and/or pressure sensor whichconforms to the shell of the machine. According to the presentinvention, various surfaces having irregular geometries may be formedinto sensor surfaces.

[0053] The present invention also provides a touch system allowinganalysis of a wave perturbation of two different types of waves, thewaves differing in mode, frequency, waveform, velocity, and/orwavelength. This system advantageously allows redundant positionmeasurement and/or differential wave perturbation sensing.

[0054] One aspect of the invention can also be described as follows.Acoustic energy is emitted into a substrate supporting propagation ofacoustic waves. This energy travels through a portion of the substrateto a receiving system, which may include redundant use of the acousticenergy emitting device. The energy is received as at least two distinctwaves. These waves have differing paths or characteristic timing. Thesewaves are non-orthogonal in either the time or space planes, meaningthat they impinge simultaneously on one or more receiving transducers,or follow paths which are substantially non-orthogonal (having arelation different than 90°).

[0055] Therefore, one embodiment of the present invention, as depictedin FIG. 7, is somewhat similar to the “triple transit” system, butallows acoustic signals following two different paths 1, 2 to bereceived simultaneously. This system provides a first path 2 with asingle reflective array 5, which reflects acoustic waves off an oppositeside 3 of the substrate 4, back through the touch sensitive region ofthe substrate, back into the reflective array 5, and to the originatingtransducer 6, with a maximum path length of about two times the sum ofthe height plus the width. The orthogonal axis receives a portion of thesame acoustic wave from the transducer 6, which reflects off a diagonalcorner reflector 7, along a perpendicular axis has a second reflectivearray 8. The wave is reflected as a set of waves 9 through the touchsensitive region of the substrate 4, and is incident on a thirdreflective array 10, which reflects the acoustic wave toward a secondtransducer 11 on an adjacent side of the substrate 4, near the firsttransducer 6. The maximum path length of this path is two times the sumof the height plus width. In this case, two transducers 6, 11 receivesignals simultaneously for at least some delay times.

[0056] Another embodiment of the invention provides a sensor whichemploys a plurality of waves having differing frequencies, wavelengths,phase velocities, or amplitude. Such waves may also be non-orthogonal inthe time or space planes, but need not be so. In other words, thesedistinguishable waves may travel sequentially and/or over orthogonalpaths.

[0057] Where portions of acoustic waves are received simultaneously by asingle transducer, it is generally preferred that a receiving circuit besensitive to a phase of a received signal in order to help resolveinterference effects. Likewise, where waves of differing frequencies areemployed, it is preferred that the receiver selectively receive thosewaves according to their frequency. Where waves of differing wavepropagation mode are employed, transducer having selectivity fordiffering waves modes may be provided. Therefore, embodiments of thepresent invention may also include a receiver sensitive to at least somewave characteristics.

[0058] A further embodiment of the invention provides a positiveresponse sensor, e.g., one where an increase in received signal isrepresentative of a typical perturbation. Typically, a perturbation in apositive response system will cause a change of some type in the wave,making it distinguishable from an unperturbed wave. Again, such a wavemay be non-orthogonal in the time or space planes, but need not be so.For example, the unperturbed signal may be completely attenuated throughfiltering, and therefore not received by the receiver. In this case,only a single, positive response signal according to the presentinvention is received.

[0059] Thus, the present invention is not limited in the conventionalmanner to sequential receipt of independent coherent signalsrepresentative of waves propagating along Cartesian coordinate axes, andanalysis thereof to determine an attenuation of a transmitted wave by atouch by detecting the energy of the wave with respect to time. Inparticular, according to the present invention, a plurality of waves maybe received simultaneously, the received signal may be an incoherentsuperposition of components from different wave sets, the waves need notpropagate parallel to a rectangular coordinate axis of a planarsubstrate, and detection is not necessarily based solely on adetermination of a time of an attenuation in power of a received signal.An improved receiver is therefore employed which includes enhancedlogical analysis of the received waveform. Advantageously the waveformsensitive analysis and enhanced logical analysis may be employedtogether.

[0060] The receipt of at least two distinct waves which overlaptemporally may indicate two waves which each have substantial energy,each being specifically intended for receipt, and potentially bearinginformation relating to a touch position along a coordinate axis.Alternately, one of the two distinct waves may be due to unintentionallyscattered waves, artifacts and interference that are not intended foruse in touch detection. In either case, a touch-information carryingsignal may be utilized even if superposed with other signal components.

[0061] The present invention allows receipt and analysis of partiallyredundant waves. Therefore, the effects of contamination and variousartifacts may be reduced. Further, where differing wave modes orfrequencies are used, a differential sensing approach may be followed todetermine both position and a mode sensitive characteristic of a touch.

[0062] The present invention includes a system in which the position ofa touch is determined by the controller independent of the physical axesof the substrate, thus providing for coordinate processing andtransformation before output. This allows increased flexibility in thelayout of the transducer systems. In this document, “transducer system”is defined to be the system that couples electronic signals to acousticwaves in the desired touch region including the transducer itself, e.g.a wedge or edge transducer, and associated reflective arrays ifemployed.

[0063] The present invention also allows receipt and analysis of signalswhich are excited by a common transducer representative of differingsets of wave paths with overlapping characteristic time-periods.

[0064] A still further aspect of the invention provides an acoustic wavetouch sensor in which a touch is detected by a perturbation of areceived signal where the perturbation may be a decrease in amplitude,an increase in amplitude, a change in phase of the received signal, or acombination of amplitude change and phase change.

[0065] One set of embodiments according to the present inventionincludes systems employing multiple waves sharing a common path portion.The known triple transit transducer also shares common path portions,but does not have simultaneously received waves or a transformation ofcoordinate system. In other words, the known triple transit systemrequires a time separation between received waves representingorthogonal axes, thus limiting the topology of the sensor.

[0066] According to one aspect of the present invention, a plurality ofwaves traveling along non-orthogonal axes in the active region of thetouchsensor may have common path portions, being at least partiallysuperposed. In particular, according to certain embodiments of theinvention, these waves will share a common transducer, and a common axisof propagation from the transducer. The waves may differ, e.g., in path,mode, frequency, phase, propagation velocity, or wavelength. Therefore,some embodiments according to the present invention provide a reflectivearray which separates the waves to propagate along differing paths.Another set of embodiments provides a plurality of sets of distinguishedreflective arrays, which reflect portions of the waves at differingangles or as waves of differing propagation modes, or both.

[0067] Sensor systems according to the present invention allowsuperposition of waves producing sets of touch-sensitive waves which aredispersed across the touch area of the substrate having characteristictime delays or other characteristics, and a system for receiving thedispersed waves and determining a characteristic of a touch or waveperturbation. The axes of propagation of one set of waves need not beorthogonal to those of another set. According to the present invention,these sets of non-orthogonal waves may be employed with orthogonalwaves. By providing more than one set of these plurality of waves, aposition of a touch may be determined using redundant information, e.g.,having more information than is necessary to mathematically determine aposition, allowing enhanced performance in the presence of noise,interference and shadowing.

[0068] As stated above, the acoustic waves may differ in otherproperties, including mode, propagation velocity, wavelength, which ingeneral provides two advantages. First, waves having differingproperties may have differing sensitivity to environmental conditionsand artifacts. Thus, the differential effect on the sensing waves may beused to determine properties of an object in contact with the surface.Further, the differences in the waves may be used to selectively filterthe waves, thus providing opportunity to selectively reduce noise orseparate potentially interfering waveforms. Waves having differingwavelength in the substrate may be selectively redirected withreflective arrays having physical characteristics corresponding to thatwavelength and its axis of propagation.

[0069] In another aspect of the invention, the coordinate system of asensing wave is non-orthogonal with an output coordinate system.Therefore, a plurality of waves must be analyzed and their positioninformation transformed in order to output a coordinate value. Theplurality of waves may also be analyzed for redundancy to verify a touchcoordinate, and potentially to resolve ambiguities, perhaps due tomultiple touches, in the two dimensional position measurement.

[0070] In an embodiment of the invention, at least three distinctacoustic wave sets are excited, of which analysis of at least two arerequired in order to detect a two dimensional position of a touch.Therefore, under various circumstances, one or more waves may be ignoredor unavailable, yet operation continues. Where at least three areavailable, the three waves may be analyzed for touch positionconsistency, artifact or interference, and to determine an optimumoutput indication of the position of the touch. The analysis of the atleast three waves may also include an output of a plurality ofsimultaneous touch positions.

[0071] According to another embodiment, differing wave modes are inducedin the substrate so that regions of low sensitivity employing onepropagation mode correspond to regions which have adequate sensitivityemploying a different propagation mode. For example, in regions whereRayleigh waves are heavily shadowed due to contamination, a lesssensitive backup wave mode, e.g. a horizontally polarized shear mode,may be analyzed for this same region to determine touch data.

[0072] The dual mode operation allows operation with at least two waves,with spatial domain, frequency domain, wave propagation mode or timedomain multiplexing. Therefore, signals may be received along differingpaths, having differing frequencies, differing wave propagation modes,or differing locations of reception.

[0073] In order to provide waves having differing characteristics fromsubstantially common sensor hardware, the signal from the transducersystem may include a number of components. In order to provide frequencymode discrimination, the receiving system must distinguish betweenvarious received frequencies. With respect to a plurality of wave modes,either the differing wave modes must be converted to a single mode whichexcites the transducer, or the transducer must be sensitive to thevarious modes. With a time domain multiplexing system, readingsaccording to various wave modes are taken sequentially. In order todetect spatially separated waves, a separate transducer may be providedor the waves may be redirected to a common receiving transducer. Wheredifferent types of waves are superposed, a perturbation will typicallyhave a different characteristic time delay for the different waves,which is used to distinguish the particular wave.

[0074] Various embodiments of the invention analyze a potentialambiguity in the received waveform. That is, two waves, followingdifferent paths, arrive at the same receiving transducer within anindistinguishable time window, and thus a given wave perturbation ispotentially attributable to either wave. Therefore, without furtherinformation, the controller might not determine, based on the signal ofthe received wave, which of the two possible paths the touch intersects.According to a subclass of these embodiments, however, a pair of suchambiguous signal perturbations occur. Thus, by analyzing the pair ofambiguous signal perturbations, with reference to a physical model ofthe sensor and additional information from signals from other wave sets,the position of the perturbation may be determined or predicted, and theambiguity resolved. Further, as referred to herein, the position may besensed unambiguously by a pair of acoustic waves emitted along a singleset of superposed arrays.

[0075] According to another aspect of the invention, additionalinformation may be obtained from an additional set of superposed arrays,e.g., along another axis. This information may be further employed indetermination of the coordinate position. More generally, the presentinvention encompasses the superposition of reflective arrays, e.g., toscatter a plurality of waves coherently, and a physically superposedarray structure.

[0076] Where the waves travel along different paths, often the waveswill be directed towards different edges of the substrate. Therefore,for example, two waves may be sensed with two different receivingtransducers simultaneously. Advantageously, therefore, a traditionaltouchscreen system and a touchscreen system with inclined propagationpaths are superposed. Embodiments according to the present invention maythus provide multiple channels for receiving acoustic wave information.

[0077] Reliability of operation is enhanced according to the presentinvention even where different types of touching objects are to besensed, such as fingers, gloved fingers, styli, etc. Likewise,potentially interfering factors may be identified and/or filtered orignored.

[0078] By allowing multiple wave modes and/or paths, the advantages ofpartially redundant measurements and differential wave perturbationcharacteristic sensing are realized.

[0079] Algorithms may use redundant coordinate information to verify andperhaps resolve ambiguities in two-dimensional position measurements.

[0080] Alternately, algorithms may support systems with redundantcoordinate measurements in which only two of three or more sets of wavesare needed to reconstruct two-dimensional coordinates of a touch.

[0081] Systems according to the present invention also encompassmultiple user touch applications. In such cases, the redundancy of themultiple wave paths may be used to resolve multiple degrees of freedom.For example, such multiple user touch systems might include a classroommulti-media device that is simultaneously hands-on for the teacher andseveral students, interactive museum displays, a two-person video gamewith a touch interface, or a large table-top display of engineeringdrawings that can be simultaneously reviewed and edited by a small groupof engineers. Complex control system human interfaces are also possible.

[0082] A multiple-user touch/display system will typically require alarger display device than a system intended for one user at a time,such as is possible with projection systems and large flat paneldisplays commercially available or under development. Therefore, variousmethods according to the present invention allow sensing of multipletouches, reduction of acoustic path lengths and of likely sources ofinterference. Embodiments according to the present invention also employaspects which allow longer acoustic path lengths.

[0083] Simultaneous touches are problematic for existing touchscreenproducts. Analog resistive, capacitive, and force-sensing touchtechnologies inherently confound a multiple touch with a false touch atan intermediate position. High-resolution resistive and capacitive touchschemes that cover larger areas with discrete touch zones become awkwardand expensive due to the large number of electronic channels required.If means are provided to resolve discrete ambiguities, acoustic touchtechnologies have the inherent capability to recognize simultaneousmultiple touches. In addition to true multiple user applications, asimultaneous touch capability would also enable touch applications inwhich a single user simultaneously touches with both hands or more thanone finger in one hand. For example, a virtual piano keyboard on atouch/display device that supports playing of chords.

[0084] It is therefore an object of the invention to provide a system inwhich waves of differing characteristics are used to sense a touch in asubstrate, wherein the waves may have differing, non-orthogonal axes ofpropagation, differing wave propagation mode, differing frequency,wavelength or phase velocity.

[0085] It is another object according to the present invention toprovide a touch sensor comprising an acoustic wave transmissive mediumhaving a surface and a touch sensitive portion of said surface; atransducer system for emitting acoustic energy into said medium; and areceiver system for receiving the acoustic energy from the substrate,for determining a perturbation of said acoustic energy due to a touch onsaid surface, said touch sensor comprising a reflective array having aplurality of spaced elements for scattering portions of an incidentacoustic wave as waves having a different propagation vector than saidincident wave and passing other portions unscattered, said array beingprovided an array selected from the group consisting of:

[0086] (a) an array associated with said medium situated along a path,said path not being a linear segment parallel to a coordinate axis of asubstrate in a Cartesian space, a segment parallel to an axial axis orperpendicular to a radial axis of a substrate in a Cylindrical space,nor parallel and adjacent to a side of a rectangular region of a smallsolid angle section of a sphere;

[0087] (b) an array situated along a path substantially notcorresponding to a desired coordinate axis of a touch position outputsignal;

[0088] (c) an array situated along a path substantially non-parallel toan edge of said medium;

[0089] (d) has a spacing of elements in said array which differs, overat least one portion thereof, from an integral multiple of a wavelengthof an incident acoustic wave;

[0090] (e) has elements in said array which are non-parallel;

[0091] (f) has an angle of acceptance of acoustic waves which variesover regions of said array;

[0092] (g) coherently scatters at least two distinguishable acousticwaves which are received by said receiving system; and

[0093] (h) combinations and subcombinations of the above,

[0094] except that said array in (d), (e) or (f) is not providedparallel and adjacent to a side of a rectangular region of a small solidangle section of a sphere.

[0095] It is also an object according to the present invention toprovide a controller which is capable of logically analyzing two sets ofwaves derived from a common transmit transducer burst which are receivedsimultaneously, i.e., in which the wave being received may not bedistinguished solely by reference to a time window. Thus, the systemneed not maintain a time separation between a plurality of waves forproper operation.

[0096] It is a still further object of the invention to provide areceiver in which a received signal is analyzed for waveforminformation, due e.g., to multipath signal paths. Further, the receiveraccording to the present invention may analyze the received signal for atouch indicated by a perturbation of complex amplitude rather thanmerely an attenuation in received power.

[0097] A further object according to the present invention is to allowoutput of a coordinate position in an output coordinate system,typically Cartesian, of a perturbation of acoustic waves, each of whichmeasures a coordinate substantially different from the axes of theoutput coordinate system.

[0098] Thus, touch position sensors according to the present inventionmay provide some or all of the following advantages:

[0099] (a) Tolerance to shadowing effects of contaminants by obtainingredundant information and/or employing robust waveforms.

[0100] (b) A higher signal to noise ratio due to availability ofredundant coordinate information.

[0101] (c) A multiple wave mode sensor allowing the composite advantagesof each selected type of wave mode, e.g., high sensitivity to touch forRayleigh wave modes, relative immunity to contaminants for horizontallypolarized shear modes.

[0102] (d) Ability to detect a mode sensitive perturbing characteristicof a touch based on differential wave perturbation and/or appearance ofa characteristic new signal.

[0103] (e) Versatility in the selection of substrate, e.g., use oflarger sizes, non-rectangular shapes, large solid angle sections ofspheres and other non-planar topologies.

[0104] (f) Ability to reliably reconstruct multiple touches and hencesupport applications in which more than one finger, hand, or user maysimultaneously input touch information.

[0105] These and other objects will become apparent from a review of thedrawings and Detailed Description of the Preferred Embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0106] The preferred embodiments of the invention will be explained byreference to the drawings, in which:

[0107]FIG. 1 is a prior art touchscreen system having a plurality eachof transmitting transducers and receiving transducers;

[0108]FIG. 2 is a prior art touchscreen system having transmittingtransducers which emit a wide acoustic wave;

[0109]FIG. 3 is a prior art touchscreen system having a divergingtransmitting transducer with a single reflective array along a curvedpath;

[0110]FIG. 4 is a prior art touchscreen system having four transducersand four reflective arrays;

[0111]FIG. 5 is a prior art touchscreen system having two transducersand two reflective arrays;

[0112]FIG. 6A is a prior art touchscreen system having six transducers,two normal arrays and two segmented reflective arrays

[0113]FIG. 6B is a touchscreen system having eight transducers and foursegmented reflective arrays;

[0114]FIG. 7 is a touchscreen system having two transducers and threereflective arrays;

[0115]FIG. 8 is a prior art triple transit touchscreen system having onetransducer and two reflective arrays;

[0116]FIGS. 9A and 9B show typical waveforms received from a transducersystem according to FIG. 4 subject to one and two simultaneous touches,respectively;

[0117]FIG. 9C shows a typical waveform received from a transducer systemaccording to FIG. 8;

[0118]FIG. 9D(1) shows the superposition of two simultaneously receivedsignals, as would be seen by summing the receiving transducers of theembodiment of FIG. 7;

[0119] FIGS. 9D(2), 9D(3) and 9D(4) show the sum of the superposedsignals of FIG. 9D(1) when the superposed signals are (2) in phase, (3)out of phase with an RMS detector, and (4) out of phase with a phasepreserving receiver, respectively;

[0120]FIG. 10 shows a generic planar sensor subsystem, withoutintermediate reflections;

[0121]FIG. 11 shows the array reflector spacing and orientation of anembodiment according to FIG. 10;

[0122] FIGS. 12(a)-(f) show example coordinate subsystem geometries asembodiment of the touchscreen system according to FIG. 10, of which FIG.12(a) is prior art;

[0123] FIGS. 13(a) and (b) show a rectangular touchscreen according tothe present invention having two orthogonal sets of wavepaths and anadditional diagonal set of wavepaths, respectively;

[0124]FIG. 14 shows a rectangular touchscreen according to the presentinvention having two orthogonal sets of wavepaths and two diagonal setsof wavepaths of which the second set of diagonal wavepaths is shown;

[0125]FIG. 15(a) shows a detail of a reflective array according to thepresent invention having two significant Fourier transform componentssupporting two distinct spacing vectors for two distinct coordinatesubsystems;

[0126] FIGS. 15(b) and 15(c) show hexagonal and triangular sensorsystems according to the present invention respectively incorporatingreflective arrays according to FIG. 15(a);

[0127]FIG. 16(a) shows a large area rectangular sensor according to thepresent invention having segmented reflective arrays;

[0128] FIGS. 16(b) and 16(c) show linear segmented reflective arrays andshingled segmented reflective arrays, respectively, according to thepresent invention;

[0129]FIG. 17 shows a generic planar sensor subsystem, similar to thesubsystem according to FIG. 10, with intermediate reflections;

[0130] FIGS. 18(a)-18(d) shows example touchscreen systems incorporatinga sensor subsystem according to FIG. 17, of which 18(c) with commontransmit/receive transducer system and 18(d) are prior art;

[0131]FIG. 19(a) shows an isometric view of a cylindrical sensor systemhaving a triple superposed array at one end thereof, according to thepresent invention;

[0132]FIG. 19(b) shows a planarized representation of the surface of thesensor system according to FIG. 19(a);

[0133]FIG. 20 shows a generic non-planar sensor subsystem, according tothe present invention;

[0134] FIGS. 21(a) and 21(b) show top and side views, respectively, of aspherical section touchsensor system, according to the presentinvention, for determining a touch position in a spherical coordinatesystem;

[0135] FIGS. 21(c) and 21(d) show flat-map projection and top views,respectively of another embodiment of a hemispherical touchsensor systemaccording to the present invention;

[0136] FIGS. 22(a) and (b) show isometric and plan views, respectively,of a Love wave mode basin sensor according to the present invention;

[0137]FIG. 22(c) shows a side view of a half-hemisphere touch sensorhaving a single transducer and reflective array system according to thepresent invention;

[0138] FIGS. 23(a)-(d) show respectively signals received fromtransducers of the embodiment according to FIG. 13;

[0139] FIGS. 24(a) and (b) show respectively a generalizedrepresentation of and a detailed specific example of flow diagrams for aredundancy check algorithm according to the present invention;

[0140] FIGS. 25(a) and (b) show respectively a generalizedrepresentation of and a detailed specific example of flow diagrams foran anti-Shadowing algorithm according to the present invention;

[0141]FIG. 26 shows a generalized flow diagram for a differential touchcharacteristic sensing algorithm according to the present invention (seeFIG. 28(c) for a specific example);

[0142] FIGS. 27(a) and 27(b) show a touch position sensor system havingtwo non-orthogonal sets of wavepaths for waves of differing modes, and atiming diagram showing the relationship of receive d signals,respectively, according to the present invention;

[0143] FIGS. 28(a) and 28(b) show a touch position sensor system havingtwo non-orthogonal sets of wavepaths for waves of a single mode and arectangular set of wavepaths for a third wave, and a timing diagramshowing the relationship of received signals for two simultaneoustouches, respectively, according to the present invention;

[0144] FIGS. 29(a)-(d) shows diagrams of the effect of a perturbation ofone of a set of superposed waves with arbitrary phase relationship;

[0145]FIG. 30 shows a typical AM receiver circuit of prior art suitablefor processing signals received by the embodiment according to FIG. 4;

[0146] FIGS. 31(a)-(f) show, respectively, alternative circuit diagramsaccording to the present invention for implementing a phase sensitivereceiver, having (a) a carrier synthesis circuit based on thetransmitted wave burst; (b) a tracking phase locked loop carrierrecovery circuit; (c) a carrier circuit which employs the transmit burstclock; (d) a clock recovery circuit based on the received signal; (e) adigital signal processor embodiment which oversamples the signal andemploys software to analyze the digitized signal; and (f) an applicationspecific integrated circuit embodiment which performs phase detection,filtering and decimation in time prior to transferring a digital signalrepresentation to a microcomputer; and

[0147] FIGS. 32(a)(1), 32(a)(2), 32(b), and 32(c) show flow diagrams ofportions of a sensor system control sequence demonstrating many aspectsof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0148] The below detailed description and examples are provided toillustrate aspects and examples of the present invention, and should notbe considered to limit various other possible combinations orsubcombinations of the elements. Therefore, it should be understood thatthe below examples are preferred embodiments or portions of embodimentswhich form a part of the invention, which is to be construed in view ofthe entirety of the specification, including relevant aspects of therecited prior art and the claims.

Overview

[0149] Acoustic Waves

[0150] The wave employed for sensing touch may be any acoustic wavewhich is detectably perturbed by a touch on a surface of a substrate.Many options exist for the choice of surface acoustic wave modes.Rayleigh waves have excellent touch sensitivity and are inherentlyconfined to a thin volume close to the touch surface even for asubstrate of an arbitrarily large thickness. Horizontally polarizedshear waves have the advantage that they weakly couple to liquid andgel-like contaminants such as water and silicone-rubber seals. Anon-homogenous substrate may support asymmetric horizontally polarizedshear waves, including Love waves, which are horizontally polarizedshear waves trapped near the touch surface like Rayleigh waves. Lambwaves in a sufficiently thin substrate provide yet another option forthe choice of surface acoustic wave mode. Various engineering trade-offsare involved in the optimal choice of acoustic mode for a givenapplication.

[0151] In this context, Love waves may be supported by a top substrateportion having a lower phase velocity interfaced with a lower substrateportion having a higher phase velocity. Similar types of waves,generally classified as asymmetric horizontally polarized shear waves,may be supported by vertical phase velocity gradients of a more complexnature. Asymmetric horizontally polarized shear waves have particularadvantages if they have essentially no power density on the lowersurface. Where Love waves are employed herein, asymmetric horizontallypolarized shear waves may be analogously employed.

[0152] The present invention seeks to enhance operation of touchscreensby providing various types of wave redundancy, wherein the redundantwave is subject to differing interferences, tradeoffs and artifacts.Thus, one redundancy strategy provides waves which propagate alongdiffering angles. Thus, a shadowing effect which reduces sensitivityalong one wave propagation axis may not also shadow a wave passing alonga different axis. A second strategy employs wave having differing modesof propagation, thus allowing the advantages of each mode to beexploited, while allowing differential detection to determine anabsorptivity characteristic of a touching object. When the differingwave modes travel along differing axes as well, further robustness isobtained.

[0153] Use of differing frequencies increases the options forimplementing wave redundancy. In addition to differentiating redundantwaves via differentiating axis or modes, different sensor subsystems maybe distinguished by narrow band filters and filtering techniques. Inaddition, by operating at differing frequencies and differing modes,physical structures of the touchscreen may be redundantly employed toreduce substrate system complexity. Furthermore, a given acoustic node,e.g. Rayleigh, at different frequencies will differ in characteristics,e.g. touch sensitivity and the amount of shadowing from contaminants, sothat use of different frequencies can serve similar purposes as the useof differing acoustic modes.

[0154] It is noted that typical known acoustic touchscreens employ twodifferent angles, e.g., X and Y axes. However, these are not consideredredundant except for the existence of a touch, rather than its position.Therefore, aspects of the present invention provide a system which iscapable of providing redundant information defining a position along atleast one coordinate axis, or a position along a coordinate axis whichdoes not correspond to an edge of the substrate.

[0155] Substrate

[0156] An acoustic touchscreen sensor is often constructed from asheet-like substrate, which is a material capable of supportingpropagation of acoustic waves with relatively low attenuation. Often,touchscreens are disposed in front of display devices, and thus they aretransparent. The present invention allows the acoustic substrate to bean integral component of a display device, such as the face-plate of acathode ray tube. The acoustic substrate may also be a touch-sensitivemechanical surface of a device, in the absence of an associated displaydevice. In circumstances where transparency of the substrate is notrequired, a metal (e.g., aluminum or steel) or ceramic substrate may beemployed.

[0157] The substrate or a component of a substrate, e.g., a portion ofan acoustic filter, may also be formed of plastic. It is noted that mostplastics are typically more acoustically absorptive than inorganicmaterials such as glass, and therefore may be unsuitable for use asmonolithic substrates for acoustic touchsensors of substantial size.However, for smaller devices, plastics may be employed as the substrateor a component of a substrate. Acoustic absorption varies greatly fordifferent polymer materials. Amongst plastics, polystyrene, low densitypolyethylene, Nylon 6/6, polypropylene, Lustran and acrylic haverelatively less acoustic absorption. For an all plastic substrate, useof such a relatively low-loss plastic is preferred. If plastic is usedto form a portion of an acoustic filter, then use of a higher-lossplastic may be permitted or even desired.

[0158] The substrate may be monolithic, laminated or coated.Non-monolithic substrates may be employed to alter a wave energydistribution in the substrate, support selected wave mode propagation,or to filter undesired wave modes. For example, a sandwich of aslow-velocity layer on a fast-velocity layer on an acousticallyabsorptive layer may support Love waves and simultaneously filter outparasitic plate waves. Thus, the substrate may comprise layers havingdiffering acoustic propagation properties and/or acoustic interfaces.

[0159] In some cases, it may be convenient for manufacturing purposes tofabricate reflective arrays on strips of material which are then bondedonto the rest of the substrate; see U.S. Pat. No. 4,746,914, column 9.Thus a laminated structure may be used for manufacturing convenience orpackaging configuration. Such laminated strips may also achieve benefitsin acoustic performance.

[0160] A sheet-like substrate, in a touchscreen embodiment for acomputer video display monitor, is commonly 2 to 3 mm thick transparentsoda-lime glass. It is noted that various substrates may provideparticular advantages for acoustic touchscreen sensors. For example,borosilicate glass has been found to have up to approximately 30 dBincreased signal-to-noise ratio over soda lime glass for a typicalRayleigh mode touchscreen system for a display monitor. Further, thereduced rate of acoustic attenuation in borosilicate glass is ofincreasing benefit as the lengths of the acoustic paths increase.Accordingly, a borosilicate glass substrate may therefore beadvantageously used for large dimension sensor systems, or those withlong acoustic wave paths.

[0161] One advantageous embodiment of the present invention provides aborosilicate glass substrate on the back of which is laminated, orotherwise provided, a projection screen. Note that the use of Rayleigh,Love and any other mode that has little energy on the back surface canbe conveniently used with a lamination or other acoustically absorptivestructure on the back surface. Known projection systems include cathoderay tubes, liquid crystal shutter devices, electro-optic projection oflaser beams, and other spatial light modulators, such as a so-calleddigital mirror device (“DMD”) from Texas Instruments. Borosilicate glassmay thus be advantageous for the large areas of image projectiondevices. In addition, the geometric flexibility of the present inventionenables considerable increase in the maximum feasible sensor size.Furthermore, such large devices may be placed in environments subject toenvironmental contamination, and therefore benefit from a robust touchsensing system as provided by the present invention, e.g., by useredundant or differential sensing of touch coordinates.

[0162] A large substrate may also be employed in a large white boardapplication, in which the substrate is touch sensitive over a largearea. In a white board application, the substrate need not betransparent, and therefore may be formed of an opaque material such asaluminum. Advantageously, aluminum and some other metals may be coatedwith an enamel with a relatively slow acoustic phase propagationvelocity, thus supporting a Love wave with high touch sensitivity(relative to horizontal shear plate-wave modes) on the front surface.

[0163] A touch sensor substrate suitable for Love waves, a shear-typewave having wave energy at one surface and substantially less on theopposed surface, is formed as a laminate of two or more substratematerials which differ in phase velocity, with the lower velocity on thetop, sensitive surface. The laminate may include a number of layers,which follow a generally increasing pattern of phase velocity change.Alternately, the laminations may have varying phase propagationvelocities, provided as a filter arrangement to particularly select adesired Love wave mode. Filtering by the substrate may be direct, e.g.,undesired modes are damped or evanescent, or indirect, phase velocitydifferences between desired mode and undesired modes are increased, thusenhancing the mode filtering performance of reflective arrays.Therefore, alternating layers of higher and lower phase velocitymaterials, with an overall asymmetry may be provided to help, e.g.,reflective arrays, select a desired Love wave. By selecting the phasevelocity distribution, the laminated substrate may selectively varyproperties of different wave modes.

[0164] An example of a Love-wave substrate with a lower velocity surfacelayer, is a 2 mm glass sheet having a uniform coating of lead-based fritof 0.1 mm thickness. Other frit or glazing options may be appropriatefor applications where acid leaching of lead from the touch surface is apotential health hazard. It is possible to construct Love wavesubstrates that strongly capture acoustic energy near the surface andhence improve touch sensitivity. For example, a 100 micron thick layerof lead-containing enamel having a shear velocity of less than about 2.6mm/μsec, on top of a 2-3 mm thick aluminum sheet with shear velocityabout 3.0 mm/μsec, captures the majority of Love-wave power within 200microns of the surface; such a substrate is very similar to a knownenamel-coated architectural aluminum panel.

[0165] Further, a glazed ceramic will also support Love wavepropagation, provided that the glaze has a reduced shear wave velocityrelative to the ceramic. Thus, for example, a basin may be formed as aplumbing fixture, e.g., a sink, or toilet bowl.

[0166] The substrate may be formed as a flat plate with a rectangularshape or a non-rectangular shape such as a hexagonal. Alternatively thesubstrate may be curved along one or both axes as a cylindrical,spherical or ellipsoidal surface or section surface, or may have otherconfigurations. In particular, large solid angle spherical, and completecylindrical substrates are contemplated. This invention providesflexibility in the layout of transducers and arrays to accommodate sucha variety of sensor shapes. For example, a polygonal touch sensor may beprovided with reflective arrays on each side and transducers at eachvertex.

[0167] Cylindrical substrates are particularly interesting applicationsof the present invention, because perimeter reflective arrays may beused without need for arrays parallel to the axis of the cylinder,allowing determination of both axial position and angle. Thus, acylindrical touch sensor may be used for electronically controllingfocus and zoom of a camera lens in a cylindrical housing withoutexternal moving parts. By employing selected wave modes having lowfractional absorption by water and a significant differential absorptionbetween water and flesh, e.g., horizontally polarized shear waves,applications such as an underwater camera control may be supported.

[0168] Reflective Arrays

[0169] Spacing-Vector Formula

[0170] Reflective arrays coherently scatter or redirect acoustic energyin a controlled fashion. Referring to FIG. 10, general principles ofreflective array design are introduced below. These very boardprinciples enable engineering of novel reflective array designs.

[0171] A comment on notation: in this document, variables which arevector quantities are given in bold face, while scalar variables arenot.

[0172] Reflector orientations and spacings can be determined from thewave vectors of the desired incident and reflected acoustic waves. Thesewave vectors are defined as follows. Let the wave vector k_(I) bedefined as parallel to the incident beam direction and as having amagnitude k_(I)=2π/λ_(I). The wavelength of the incident beam,λ_(I)=v_(I)/f, is determined from the operating frequency, f, and thephase (not group) velocity, v_(I), of the incident wave. Likewise forthe reflected wave, let us define k_(R) be defiled as parallel to thereflected beam direction with magnitude k_(R)=2π/λ_(R) whereλ_(R)=v_(R)/f with v_(R) being the phase velocity of the reflected wave.

[0173] These wave vectors may be a function of position along the array.For this purpose we introduce a path parameter “s” which uniquelyidentifies members of sets of acoustic wave paths, and hence also theposition along arrays at which the acoustic path is scattered from thetransmit array or scattered onto the receive array. For example eachmember of the set of acoustic paths can be represented by a value of “s”between zero and one. In general, the incident and reflected wavevectors for an array are functions of s: k_(I)(s) and k_(R)(s). For asensor system as described in U.S. Pat. No. 4,645,870, in which thevalue of s for a touch is identified by the frequency of the signalabsorption, even the operating frequency, f(s), and hence thewavelengths, λ_(I)(s) and λ_(R)(S) , depend on the path parameter. Fornotational convenience, the path parameter dependence is not alwaysexplicitly written and is implicitly implied. In many cases, such asflat rectangular sensors of the prior art, the wave vectors areconstants that do not depend on the path parameter.

[0174] The spacing and orientation of the array reflectors, for eachposition along a reflective array, can be determined from the wavevectors k_(I) and k_(R). Consider, for example, the case where thereflective array is composed of line-segment reflector elements; seeFIG. 11. Of particular interest is the reflector spacing vector S whichis perpendicular to the reflector lines and has a length equal to thecenter-to-center spacing between reflector elements in a directionparallel to S. If the reflector spacing vector S is known, then so arethe orientations and spacing of the reflectors.

[0175] It is noted that the line-segment reflector elements representedin FIG. 11 are a form of pulse compression filter, and other known typesof such pulse-compression filters may be employed according to thepresent invention, as appropriate.

[0176] The spacing vector, which in general is a function of the pathparameter, may be determined from the incident and reflected wavevectors as follows.

S=2πn (k _(I) −k _(R))/|k _(I) −k _(R)|²

[0177] This is the fundamental equation of coherent reflective arraydesign. All reflector element orientations and spacings found in theprior art can be derived as special cases of this general formula.Furthermore, this fundamental equation enables the design of arrays forlarge families of new sensor embodiments outside the scope of prior art.Given its importance, the derivation of this spacing-vector formula ispresented is some detail below.

[0178] For the derivation, we define a reflector orientation vector Rwhich is parallel to the reflector line elements and whose length is thedistance from point A to point C in FIG. 11. The reflector spacingvector S is perpendicular to the reflector elements; in vectordot-product notation, this orthogonality condition is expressed asR·S=0.

[0179] Note, for example, that k_(I)·R=(2π/λ_(I))×R×cos(θ) where θ isthe angle defined by the points A, C, and F. R×cos(θ) is the extradistance the incident acoustic wave must travel to intercept thereflector at point C rather than point A. Hence (2π/λ_(I))×R×cos(θ) isthe phase advance, in radians, of the incident acoustic mode inpropagating from point F to point C.

[0180] Similarly k_(R)·R is the phase advance for the reflected acousticmode propagating from points A to G.

[0181] Coherent scattering from arbitrary pairs of points within a givenreflector element, e.g. points A and C, requires equality of the phasedelays k_(I)·R and k_(R)·R. This requirement can be expressed as(k_(I)−k_(R))·R=0, that is, the reflector elements are perpendicular tothe vector difference of the incident and reflected wave vectors.

[0182] If there is no mode conversion, and hence the wave vectors k_(I)and k_(R) have the same magnitudes, (k_(I)−k_(R))·R=0 reduces theangle-of-incidence-equals-angle-of-reflectance rule familiar from theoptics of mirrors. If there is mode conversion, then the angle ofincidence no longer equals the angle of reflectance, but rather isquantitatively analogous to Snell's law familiar from refraction inoptics (where phase velocity equals the speed of light divided by theindex of refraction).

[0183] Note that because vectors S and (k_(I)−k_(R)) are bothperpendicular to the reflector elements, both are orthogonal to R. Hencethey must be parallel to each other (the algebraic sign of ±S isphysically irrelevant, so there is no loss of generality if we neglectthe possibility that they are anti-parallel). This confirms that thespacing-vector formula correctly gives the spacing vector direction.

[0184] Now consider the requirement that scattering between arbitrarypoints on different reflectors be coherent. In particular, considerscattering from points B and C in FIG. 11. The phase delay for theincident wave propagating from points D to B can be shown to equalk_(I)·S. The phase delay for the scattered mode to propagate from pointsB to E is −k_(R)·S. Hence the total phase delay for scattering off ofpoint B relative to scattering off of point C is (k_(I)−k_(R))·S. Tohave coherent scattering between reflector elements, this total phaseadvance must be an integer multiple of 2π, and hence the condition(k_(I)−k_(R))·S=2πn.

[0185] Together, the within-reflector-coherence condition,(k_(I)−k_(R))·R=0, and the between-reflector-coherence condition,(k_(I)−k_(R))·S=2πn, tells us that (k_(I)−k_(R)) is parallel to S andhas a magnitude of 2πn/S. Hence we have the following equality.

(k _(I) −k _(R))=2πnS/S ²

[0186] Solving for S gives the fundamental spacing-vector formula givenabove.

[0187] A given spacing vector S will support scattering in the reversedirection. More formally, if we define the reverse-direction wavevectors k_(I)′=−k_(R) and k_(R)′=−k_(I) then a spacing vector Ssatisfies the spacing-vector formula for k_(I) and k_(R) if and only ifit satisfies the spacing-vector formula for k_(I)′ and k_(R)′.

[0188] A special case of a spacing vector is an “n=1 spacing vector”which satisfies the following relation that does not contain a factor“n”.

S=2π(k _(I) −k _(R))/|k _(I) −k _(R)|²

[0189] From a mathematical perspective, this is the most fundamentalform of the spacing vector formula. Mathematically, a reflective arraywith a spacing vector of S is typically a superposition of a componentswith spacing vectors of S/2, S/3, etc. The n>1 solutions result fromcoherent scattering off of these “higher harmonics” of the basicreflector spacing.

[0190] Definition of Reflective Array

[0191] Reflective arrays in known systems and available touchscreenproducts are composed of line-segment reflective elements composed ofmaterial deposited on the substrate surface, fabricated by removingmaterial from the substrate surface, or combinations of both. Here wedefine a reflective array more generally to be a region of a sensorsubsystem in which the acoustic properties of the medium have beenmodulated in such a fashion to produce a distribution of scatteringcenters which has a significant two-dimensional Fourier-transformamplitude for the point in two-dimensional wave-vector space given by2πS/S² where S is a desired n=1 spacing vector. This condition assurescoherent scattering in the desired direction into the desired acousticmode.

[0192] In a preferred embodiment, reflective arrays are composed oflinear reflector elements as illustrated in FIG. 11. The reflectivearrays may be formed by any means that alters the acoustic impedance ofthe substrate for the incident acoustic waves. In a preferredembodiment, reflector elements are raised lines formed by screeningglass frits through a stencil on the surface of the substrate andsubsequently firing the screened substrate to fuse the frit to thesubstrate. In another embodiment, the reflectors are depressions in theacoustic substrate, perhaps back-filled with another material.Manufacturing cost considerations often guide the choice amongst themany options here.

[0193] While the general definition of reflective arrays includes arraysof line-segment reflectors in which the shortest distance betweenreflectors is given by the desired n=1 spacing vector S or a multiplethereof, this is not a requirement. For example, in analogy with crystaldiffraction of neutrons off of nuclei, a reflective array may becomposed of an array of reflective dots. X-ray crystal diffractionprovides an analogy where the distribution of scattering centers(probability densities for electron orbitals) is more complex;reflective arrays need not be divisible into well-defined or isolatedreflective elements. For example, a ductile substrate surface, e.g.aluminum or temporarily heated glass, may be modulated in a sinusoidalor more complex fashion by a stamping process. The coherent scatteringprinciples in the spacing-vector formula are independent of the detailsof reflective array fabrication techniques.

[0194] Many embodiments involve superposed reflective arrays. Thegeneral definition of a superposed array is a region of a sensorsubsystem in which the acoustic properties of the medium have beenmodulated in such a fashion to produce a distribution of scatteringcenters which has significant two-dimensional Fourier-transformamplitudes for two or more points in 2-D wave-vector space given by2πS_(i)/S_(i) ² where S_(i) for i=1,2, . . . are two are more desiredn=1 spacing vectors.

[0195] As stated above, other types of pulse compression filters may beemployed to redirect or scatter portions of the acoustic wave alongdesired paths or sets of paths. Generalizing, therefore, the pulsecompression filter has at least one two dimensional Fourier transformwith an admittance for a desired wave or set of waves. Examples of theseother types of pulse compression filters are employed, for example, inthe field of piezoelectric radio frequency surface acoustic wave (SAW)devices.

[0196] Shared Wave Paths

[0197] In order to simplify the construction of the system or to supportmore compact sensor designs, a plurality of desired waves may sharephysical elements and portions of wave paths. In order to create asystem in which a plurality of sensor subsystems share portions of wavepaths, a number of configurations are possible.

[0198] First, a reflective array having a set of reflective elementswith a characteristic spacing and angle which is suitable for scatteringtwo different waves may be employed to generate two sets of wave paths,which are ultimately analyzed. Thus, the same physical elements of thereflective array may be used to reflect both waves. Generally, suitablewaves may differ in frequency and/or wave mode. Referring to FIG. 11,this is the case in which a single spacing vector, S, simultaneouslysatisfies the spacing vector formula for two or more combinations ofincident and reflected wave vectors; the value of n need not be the samefor the two or more combinations. While this approach provides anelegant economy of design, the spacing-vector formula places constraintsthat limit the geometrical flexibility of this approach.

[0199] Second, a plurality of arrays may be provided, adjacent to eachother, as shown in FIGS. 18(a), and (c). In this case, each array may beprovided with a separate transducer or a transducer wide enough toexcite acoustic waves propagating through more than one array. Thespatial separation of the arrays provides opportunity for filtering ofthe wave between the arrays to remove undesired components. A wave froma lateral array must pass through a medial array in order to travel toor from the central, touch sensitive region. Scattering from undesiredarray may lead to some loss of signal amplitude and perhaps generationof parasitic acoustic paths; typically this will be a minor effectbecause only a small portion of the wave will be scattered by each arraythe wave passes through. If necessary, various parasite suppressiontechniques discussed below may be applied. For applications with tightspace constraints, this approach has the disadvantage that the regioncontaining the arrays near the edge of the substrate may need to berelatively large.

[0200] Third, arrays may be placed on opposite faces of the substrate.In this case, the waves intended for interaction with the reflectivearrays on the back of the substrate must have a significant powerdensity on the rear surface of the substrate, as is the case for platewaves. For example, A reflective array on the top surface may have aspacing vector designed for Rayleigh-to-Rayleigh scattering, and a rearreflective array may have a spacing vector designed to couple a HOHPSwave in the touch region to a back-side Rayleigh wave. This approachcontrasts with the top-and-bottom array schemes proposed for Lamb wavesensors in order to distinguish symmetric and antisymmetric Lamb waves,allowing one to assure that only one acoustic mode is emitted; see U.S.Pat. Nos. 5,329,070, 5,243,148, 5,072,427, 5,162,618, and 5,177,327.

[0201] Fourth, a plurality of reflective elements arranged as arrays maybe superposed in the same physical space, or more generally thereflective array may be designed by whatever means to support more thanone spacing vector, as shown in FIG. 15(a). This configuration isgenerally preferable, because of its efficient use of spacing, efficientuse of transducers and corresponding wiring and electronics. If thediffering acoustic modes propagate along the superposed arrays, e.g.,Rayleigh and shear, distinct transducers may be required.Advantageously, where the arrays are physically superimposed and only asingle mode is propagated along the array, a single transducer may beemployed.

[0202] Reflective Boundaries as Example of Reflective Array

[0203] The acoustic path may encounter a reflective boundary betweenscatterings off of the transmit and receive arrays. This is thegeneralized concept shown in FIG. 17. The reflective boundary mayutilize coherent scattering from a superposition of scattering centers,and if so can be designed using similar principles as for reflectivearrays that follow segments of acoustic paths. For example, the spacingvector formula can still be applied. Note, however, that for reflectiveboundaries, it may be advantageous to use reflective elements thatscatter more strongly.

[0204] In many cases, a reflective boundary enables common or superposedtransmit and receive arrays. For example, consider a superposedreflective array on a flat substrate including elements disposed atangles of 45°±θ. Thus, waves propagating along the array will bescattered at angles of 90°±2θ. Where a reflective Structure is disposedopposite and parallel to the superposed reflective array across thesubstrate, and the reflective boundary's spacing vector is perpendicularto the boundary, waves will travel in sets triangular paths.

[0205] Under certain circumstances it may be desired to alter a wavemode while reflecting from a reflecting structure, rather than at thereflective array. In this case, the reflective structure may be providedas a series of appropriately spaced parallel elements which togetherefficiently scatter the wave energy as a selected mode; thecoherent-scattering, condition of FIG. 11 applies to reflectiveboundaries as well as reflective arrays. For example, a variant of thetriangular acoustic paths above is one in which the reflective boundaryand one of the sets of reflectors of the reflective array are designedas mode converters.

[0206] Parasitic Acoustic Paths

[0207] Engineering care may sometimes be required in array design tominimize creation of undesired parasitic acoustic paths which can resultin signal artifacts. There are many means available to suppress suchparasitic signals.

[0208] The reflective arrays serve as narrow band filters for bothwavelength and angle of propagation. Thus, a reflective array has a highdirectional sensitivity, which in conjunction with the transducer'sdirectional sensitivity, serves to limit the angular acceptance of thesystem. Thus, stray wave energy rarely causes substantial interferencein the received electronic signal.

[0209] In cases were a parasitic acoustic path has a delay time longerthan the delay times of the desired signals, the parasitic signals maybe eliminated by time gating of the received signals.

[0210] The elements of the reflective array are designed to beinefficient reflectors, i.e., they allow a substantial portion of thewave to pass unscattered, with a small portion being scattered accordingto known principles. In a preferred array design, of order 1% ofincident wave energy is scattered at elements of an array. Since thereflective elements each reflect of order 1% of the incident waveenergy, reflected waves which are not directed directly toward thereceiving transducer will require an additional reflection, andtherefore will be substantially attenuated as compared to a desiredsignal. Studies by the present inventor have determined, in fact, thatthe primary interference due to stray acoustic energy is related toparasitic paths having a small number of reflections in its wave path,rather than scattered wave energy having elongated paths involvingmultiple reflections. Thus, interference may be controlled by attentionto a relatively small number of direct parasitic paths rather than alarge number of indirect paths.

[0211] Another result believed attributable to the relatively lowreflectivity of the reflective elements and arrays as a whole is thatsmall signal presumptions, e.g. the principle of superposition, arevalid when analyzing the reflective arrays. Thus, the present inventorhas found that low reflectivity reflective arrays, when overlayed,superpose generally linearly, without significant higher order effects.Thus, the intersections of the overlayed elements, as well as potentialresonances, did not result in artifacts, distortion, undue parasiticpaths or inoperability.

[0212] Signal Equalization Methods

[0213] Controller electronics and associated touch recognitionalgorithms typically can accommodate variations in signal amplitudes(before a touch) without variation in the touch sensitivity as perceivedby a user. There is always a limit to the dynamic range of amplitudesthat can be thus accommodated. Hence, it is generally desirable to limitthe dynamic range of signal amplitudes within the useful time window ofa received signal for the set of acoustic paths of a sensor subsystem.The variation is signal amplitudes can be controlled by a number ofsignal equalization methods.

[0214] Below a number of signal equalization methods are described.Combinations of these methods may be used simultaneously.

[0215] The power density of reflected acoustic waves may be controlledby a “reflective element withdrawal” method, as discussed in U.S. Pat.No. 4,644,100 and Re. 33,151. Here the spacing of reflector elements isvaried. Here the “n” in the spacing vector formula, and hence the seriesof discrete options for the spacing vector S compatible with desiredincident and reflected wave vectors, is used advantageously as a locallyvarying array parameter. The “reflective element withdrawal” method issuch that selected reflective elements in the array are eliminated froma nominal dense n=1 array. It is noted that for superposed or dual usearrays, the optimal reflective element placement may vary from thatprovided for simple reflective arrays.

[0216] Note that with the withdrawal method, the local spacing vector isincreased in length by an integral multiple, e.g., m. This increase inspacing makes it more likely that coherent parasitic scattering willtake place because withdrawn reflectors are no longer available toprovide destructive interference for undesired scattering. Moreformally, an integer value for n′ may exist for a parasitic scatteredwave vector k′_(R) for a value of m greater than one, where no suchsolution exists for m=1:

mS(s)=2πn′(k _(I) −k′ _(R)(s))/[(k _(I) −k′ _(R)(s))·(k _(I) −k′_(R)(s))]

[0217] In cases where this proves to be a significant cause of parasiticsignals, alternate signal equalization techniques are preferred.

[0218] Another method of obtaining constant power density includesvarying the power reflectivity at points along the array by providing avariable height reflective elements. Such reflecting elements ofreflective arrays having varying height are known, see U.S. Pat. No.4,746,914, incorporated herein by reference.

[0219] A further method of modulating reflected power is the use ofsegmented or truncated reflective array elements, having interruptedreflective elements, e.g., dashed or dotted lines, or staggered lines.See, U.S. Pat. Nos. Re. 33,151, and 4,700,176, FIGS. 9, 10 and 10 a, andaccompanying text, incorporated herein by reference.

[0220] A still further method of modulating reflected power is to varythe line width of reflector lines. A reflector element of finite widthcan be analyzed as a superposition of many adjacent reflector elementsof infinitesimal width. The scattering amplitude for the finite widthreflector is the vector sum of the scattering amplitudes of itsinfinitesimal elements. In known sensors, the line width of thereflector element is designed so that there is a 180° path-length phasedelay between the scattering off of the first and last infinitesimalreflector elements of the line width; and hence the line width is chosento maximize the scattering amplitude. Therefore, the present inventionencompasses a new reflected power modulation technique, that ofreflective element line-width modulation. This method has an interestingbenefit in the context of the present invention; for some parasiticscatterings, it is possible to pick a line width that substantiallyeliminates the parasitic scattering amplitude and yet supports a usefulscattering amplitude for the desired signal path. This method is alsoadvantageous for superposed reflective arrays because it allowsmodulation of reflected power while maintaining a uniform fritthickness. More generally this method supports array designs suited tomanufacturing processes that support only one modified acousticimpedance of the substrate.

[0221] Segmented Reflective Arrays

[0222] In order to reduce an acoustic path length in large substrates, aside of a substrate mat be subdivided into a plurality of segments, eachwith its own transducer and reflective array associated with thattransducer, as shown in FIGS. 6(a) and (b) and 16(a)-(c). Thus, anacoustic wave path need not include the length of an entire side of asubstrate. Where the side is bisected, in a known embodiment shown inFIG. 6(a), the two transducers may produce or receive waves traveling inantiparallel directions along a reflective array which is provided astwo reflective arrays which each reflect an acoustic wave directly intoa touch sensitive portion of a substrate. The two reflective arrayportions overlap slightly, so that the overlapping portion is sensed byparallel waves of the same type produced by two transducers.

[0223] More generally, a reflective array may be segmented and disposedalong a perimeter of an active region of a substrate. In this case, eachsegment includes a transducer at one terminus. According to thissegmented array arrangement, the acoustic wave path length is reduced tothe distance across the substrate plus the lengths of the transmittingand receiving arrays, which are shorter than the length of the substrateon the side where the arrays are situated.

[0224] Segmented arrays 1601 may lead to blind spots 1602 in a compositesystem at the junction of adjacent segments, as shown in FIG. 16(b). Insome cases of sufficiently redundant sensor systems, such blind spotsmay be acceptable. In other cases blind spots may be avoided byarranging the reflective arrays to be shingled, i.e., inclined andoverlapping a small amount at respective ends, as shown in FIG. 16(c),with the end of the array 1603 associated with the transducer 1604 beingplaced behind another array 1605. In this case, the angles and spacingof the reflectors should be adjusted as compared to a non-inclinedarray, per the principles of FIGS. 10 and 11, to provide wavespropagating along desired axes. In a special case noted above, as shownin FIGS. 6(a) and 6(b), two end-to-end arrays 12, 13, 14, 15 (withantiparallel propagating waves) may avoid a blind spot by providing anoverlapping portion 16, 17, but this solution is only applicable tofront-to-end bisected systems.

[0225] Reverse Reflection

[0226] In some cases, it may be advantageous for an array to direct anacoustic path away from the touch region towards a reflective boundary,and hence only indirectly couple to acoustic path segments across thedesired touch region. U.S. Pat. No. 5,260,521, incorporated herein byreference, in particular FIG. 17 and accompanying text thereof,illustrates such an arrangement. As shown in this prior art example,such reverse reflection provides additional opportunities to includemode-selective filtering within the acoustic path. It is noted that,according to the present invention, the reflective boundary according tothe present invention need not comprise an edge of a substrate or beparallel to an edge of the substrate and/or a reflective array.

[0227] It the context of the present invention, reverse reflection mayoffer another possible benefit. If a desired spacing vector of asuperposed a array

S=2πn(k _(I) −k _(R))/|k _(I)−k_(R)|²

[0228] contributes to an undesired parasitic acoustic path, reversereflection can allow use of a similar set of acoustic wave paths in thedesired touch sensitive region of the sensor while employing acompletely different direction for the spacing vector, due to a reversalof for the scattered wave vector. This adds to the design optionsavailable to suppress parasitic paths.

[0229] The reflective portion may be a cut edge of the substrate, or oneor more parallel reflective elements providing a highly reflectiveinterface for the desired wave(s). These reflective elements may beformed in similar manner to the reflective elements of the reflectivearrays, although for increased reflectivity, a relatively largescattering strength is preferred. Advantageously, a reflective structuremay be provided which controls an angle of reflection, thereby reducingreliance on the edge condition of the glass, and allowing fine controlover the propagation angle of each wave path.

[0230] Reverse reflection typically adds to the acoustic path length andhence adds to the delay times. In some cases, this may provide means toavoid time overlap between signals from two sensor subsystems.

[0231] Under certain circumstances it may be desired to alter a wavemode while reflecting from a reflecting portion. In this case, thereflective portion may be provided as a series of parallel elementswhose spacing satisfies the vector-spacing formula for the desiredscattering of incident wave energy into the selected mode.

[0232] In various sensor configurations, the desired touch sensitiveportion of a substrate may be disposed as desired, for example medial orlateral to a reflective array with respect to a boundary of thesubstrate.

Electronics

[0233] Transducer Interface

[0234] The transmitting and receiving transducers couple electricalenergy to and from the controller to acoustic energy in the touchscreen.While other types of transducers are possible, transducers based onpiezoelectric elements are generally preferred for reasons of cost,mechanical compactness, and performance.

[0235] A piezoelectric element is typically in the form of a thinrectangular slab having conductive portions serving as electrodes on twoopposing surfaces. When an oscillating voltage signal is applied to theelectrodes, the resulting electric field within the piezoelectricmaterial, via the piezoelectric effect, causes the element to vibrate.Conversely, if the element is subjected to mechanical oscillations, anoscillating voltage will appear on the electrodes.

[0236] There are several options regarding the mode of the piezoelectricelement's mechanical oscillations. A common choice is the lowest-ordercompression-expansion oscillation with respect to the thin dimension ofthe element; such an element couples to bulk pressure waves or otheracoustic modes with a significant longitudinal component. Another optionis a lowest-order shear oscillation in which one electrode-bearingsurface moves anti-parallel to the opposite face; such an elementcouples to bulk shear waves and other acoustic modes with shearcomponents. The direction of shear motion can be designed to be anydirection within the plane of the electrodes. More complex options arealso possible. According to one aspect of the present invention, varioussets of sensing waves propagating in the substrate may be distinguishedaccording to their propagation mode by selective coupling to appropriatemode-sensitive transducers.

[0237] Typically, piezoelectric elements are designed to have a resonantfrequency at the operating frequency for the desired mode ofoscillation. For lowest order compression oscillation, the resonantfrequency is the bulk pressure-wave velocity (in the piezoelectricmaterial) divided by twice the piezoelectric element thickness so thatthe piezo transducer element is a half wavelength thick. Similarly, alowest-order shear-mode piezoelectric element is half of a bulk-shearwavelength thick. As used in a touchscreen, the piezoelectric element isa damped mechanical oscillator due to coupling to acoustic waves in thesubstrate. The mechanical quality factor, Q, is typically in the rangefrom 5 to 20. Viewed as a frequency filter, the piezoelectric elementhas a corresponding relatively broad bandwidth; two signals atfrequencies that are considered distinct by controller receivercircuitry might still use a common transducer.

[0238] A piezoelectric element may be bonded directly to the touchscreensubstrate and thus form a transducer. For example, see FIG. 2B of U.S.Pat. No. 5,162,618, incorporated herein by reference in its entirety.Such transducers are typically placed on the edge of the substrate andreferred to as “edge transducers”. A transducer may include more thanone piezoelectric element which may help coupling to the desiredacoustic mode; for example see FIG. 2D of U.S. Pat. No. 5,162,618. Alltransducers shown in FIG. 2 of U.S. Pat. No. 5,162,618 may be used withthis invention.

[0239] The piezoelectric element may be coupled indirectly to thetouchscreen substrate. For example, see the “flexible connector” thatserves as an acoustic transmission line between the piezoelectricelement and the substrate in FIG. 12 of U.S. Pat. No. 5,072,427,incorporated herein by reference in its entirety.

[0240] In a preferred embodiment, the transducer includes a wedge shapedcoupling block between the piezoelectric element and the touchsubstrate. When used as a transmitting transducer, the piezoelectricelement generates bulk waves in the wedge material which in turn coupleto the desired acoustic mode in the touch substrate. For example, incommercial touchscreen products of Elo TouchSystems, pressure-modepiezoelectric elements are coupled to Rayleigh waves in this fashionwith an acrylic wedge. Alternatively, a wedge transducer may couple ahorizontally polarized shear piezoelectric element to Love waves in asuitable touch substrate. The wedge material must have a bulk waveacoustic velocity that is slower than the phase velocity of the desiredmode in the touch substrate; the cosine of the wedge angle equals theratio of these two velocities.

[0241] The receiving transducer may also serve as the transmittingtransducer in certain embodiments. When the same transducer is used forboth transmission and reception, the low-voltage high-sensitivityreceiver electronics may be temporarily disconnected through a highimpedance switch from the higher voltage transmitting electronics.

[0242] The transmitting transducer receives a sine wave or pseudo sinewave tone burst at the desired frequency, from the controller. Thisburst typically has a power spectrum with a maximum at a nominaloperating frequency. Normally, the sensor is tuned for use at a specificfrequency or set of frequencies, and therefore this parameter ispredetermined. See, U.S. Pat. No. 4,644,100, Re. 33,151, and U.S. Pat.No. 4,700,176, incorporated herein by reference.

[0243] Piezoelectric transducers of the type described are inherentlydirectional. Acoustic-electronic coupling is strongest when all parts ofa piezoelectric are driven, electronically or mechanically, in phase.Thus, waves which are incident at a skewed angle to the face of thepiezoelectric element, have a substantially reduced off axis response.

[0244] Typically, transducers are mode selective. For example, a wedgetransducer with a pressure-mode piezoelectric element may be sensitiveto Rayleigh waves but insensitive to horizontally polarized shear waves.A transducer based on an edge mounted horizontally-polarized shear modepiezoelectric element may be sensitive to ZOHPS waves but insensitive toLamb waves. The mode selectivity of transducers contribute to thesuppression of signals from parasitic acoustic paths.

[0245] It is noted that, as used herein, the transducer system comprisesthe transducer and any associated array. Therefore, the transducersystem generates sets of incrementally varying waves traveling throughthe substrate, which may be of the same or different wave propagationmode as generated by the transducer itself.

[0246] Control System

[0247] The control system has a number of functions. First, anelectronic signal is generated, which excites the transducer to generatean acoustic waves which subsequently form the sets of waves. Atransducer then receives the sets of waves, and transduces them to anelectrical signal. The electrical signal is received, retainingsignificant information with a relatively high data rate in a low levelcontrol system. An intermediate level control system, often combinedstructurally with the low level control, processes the received data,seeking to identify and characterize perturbations. For example, in oneembodiment, the intermediate level control filters the signal, performsbaseline correction, and determines a relation of the signal to athreshold. A high level control analyzes the signal perturbations andoutputs a touch position. The control system as a whole therefore hasthe functions of exciting an acoustic wave, receiving portions of theacoustic wave bearing touch information as a perturbation, and analyzingthe received portions to extract characteristics of the touch, e.g.,position.

[0248] In a preferred embodiment, as discussed in detail below, theelectronic signal exciting the transmitting transducer is in the form ofa short tone burst and delay times are determined for perturbations inthe received signals. Alternately, the control system may determinewhich wave paths are absorbed by a touch via a frequency analysis ofsignal perturbations. Sec, e.g., U.S. Pat. No. 4,645,870.

[0249] A. Implementations

[0250] A typical control system for a touch position sensor includes adigital microcomputer system having program instructions stored in anon-volatile memory. This, for example, is an 8 or 16 bitmicrocontroller having internal CPU, RAM, counters and timers andpossibly other functionality. Thus, an industry standard 80C51derivative microcomputer or an ASIC device including an 80C51 core maybe used. Likewise, a digital signal processor may be employed foranalysis of the waveforms, or a low cost RISC microcontroller such asthe Microchip PIC 16X and 17X RISC microcontrollers may also beemployed.

[0251] The circuitry to implement the control according to the presentinvention may be provided as discrete devices, standard devicespartitioned according to general availability, or as highly integratedcircuits such as application specific integrated circuits (ASICs). Apreferred control circuit is provided as a pair of ASICs which aregenerally involved in digital control of burst and acquisition cycles,and analog transmit and receive functions of the touchscreen systems,respectively. Traditionally, the excitation necessary for piezoelectrictransducers in acoustic touchscreens has required relatively highvoltages in the tens of volts range, and therefore discretesemiconductor devices were employed for this function. However,according to several embodiments of the present invention, a logic leveltransducer excitation is possible, permitting highly integrated mixedsignal ASICs to implement the control. Therefore, the present inventionalso encompasses a highly integrated control circuit to implement theexcitation and receive functions, and optionally the programmablemicrocontroller. Logic level voltages are intended to mean signalsintended for communication between digital integrated circuits.Therefore, one advantageous embodiment may include excitation usingvoltages intended for intercomputer device communication, which maytypically have higher voltages than intracomputer communicationsdevices. Thus, such voltages may be derived from an RS-232communications circuit, such as may be used to communicate touchposition output.

[0252] While the various functions of the control are described hereinseparately, it should be understood that in many instances, a high levelof functional integration is preferred, and therefore it is understoodthat common hardware elements may be used for the various functions.However, in some instances, especially where the touch sensing systemsare employed with host computers, some of the high level functions maybe implemented on the host computer as a program or so-called devicedriver.

[0253] B. Excitation

[0254] The excitation function is generally straightforward. A series ofpulses or shaped pulses are emitted in a defined pattern, havingsubstantial power spectrum density at a nominal operating frequency offrequencies. Because this pulse is of limited duration, it has a finiteband width. For example, Elo TouchSystems manufactures a controllerwhich can excite 5.53 MHz tone bursts with durations in the range of 6to 42 oscillations. This electronic pulse train drives a transmittransducers which emits acoustic waves traveling away from thetransmitting transducer. The wave is highly directional, and travelsalong an axis, which for example passes through a reflective array.

[0255] Where high flexibility of control over the excitation burst isdesired, a direct digital synthesizer, such as the Analog Devices AD9850may be employed.

[0256] During the excitation, it is generally desired that the receivingcircuitry, which may be multiplexed to receive signals from a pluralityof transducers, be electrically isolated, e.g., through electronicswitches and/or diodes, so that parasitic electrical paths from theexcitation circuitry do not overload the high gain receiver circuitry orinfluence charge storage elements including filters. When the excitationpulse is finished, the receiving circuitry is then connected to thereceiving transducer, which may be the same as the transmittingtransducer, by electronic switches. The isolation circuitry maycooperate with the multiplexing circuitry. The excitation circuitry maybe adaptive to accommodate variations in the characteristics of thesensor subsystems. For example, Elo TouchSystem controller productE281-2310 adapts to touchscreens of varying signal attenuations byadjusting the burst pulse duration.

[0257] C. Bandwidth Considerations

[0258] The excitation tone burst is of finite duration and will henceinclude a number of frequency components including the nominal transmitfrequency. This frequency spread is typically broad compared to therelatively narrow frequency filtering characteristics of the reflectivearrays.

[0259] The reflective arrays act as filters, and are generally thenarrowest band filtering system of the transducer. For well equalizedsignal amplitudes and for high quality array design and manufacturingcontrol of reflector spacings, the band width can approach thetheoretical limit proportional to the inverse of the signal duration.Thus, much of the broadband energy from the excitation pulse is notcoherently scattered or is misdirected by the reflective arrays and notreceived with the desired signal(s). In some cases, components of thebroadband wave energy may lead to parasitic signals due to sidelobes,mode conversion, or other undesired effects which allow this wave energyto interfere with receipt of the desired waves. This provides amotivation to limit the bandwidth of the receiving circuitry. Thus, thereceiver may include a selective filter.

[0260] From a frequency-domain perspective, a touch alters the frequencyfiltering characteristics of the sensor subsystem A perturbation due toa touch which is narrow in the time domain will lead, via thefundamental mathematical relationships between bandwidth and timeduration, to a broadening of the frequency filter characteristics of thesensor subsystem The transmitted tone bursts are generally kept shortenough so that the sensor subsystem is excited for the band offrequencies containing the touch information. The bandwidth of thebandpass filters in the receiving circuitry must have sufficient widthto pass frequency components containing the touch information.

[0261] D. Receiver

[0262] The control receives the signals corresponding to the acousticwaves from the transducer and processes the signals for analysis. Thecontrol retains relevant data and may, and indeed preferably, filtersextraneous data from the signal. Thus, where the relevant information istime and amplitude for a smoothed wave-form, other information may beignored such as phase, frequency components outside the desiredbandwidth, and signals for receive transducers for other sensorsubsystems. Further, the type of data contained in the signal definesthe simplest acceptable controller configuration. However, other typesof information may also be included within the signal. Analysis of thisinformation may be useful in analyzing the signal. The purpose of thereceiver is to extract information from an acoustic wave signal whichmay represent its source, path, characteristics or type ofperturbation(s), timing of perturuation(s), duration of perturbation(s),frequency characteristics of perturbation(s), pressure or amplitude ofperturbation(s), and interferences or artifacts. Thus, the receivertakes a signal having a large amount of raw data and produces vectorsrepresenting significant features of the signal.

[0263] According to certain embodiments of the present invention,different types of waves may be time multiplexed, e.g., applied to thesubstrate sequentially, and therefore need not be present or analyzedsimultaneously. Thus, where excitation of transmitted waves havingdiffering frequencies or wavelengths may be independently selected,these may be time multiplexed onto the substrate. Therefore, a receivermay also be multiplexed to operate in a plurality of states.Alternately, various wave modes may be simultaneously applied to thesubstrate and resolved by selecting one of two or more receivetransducers receiving signals from a common transmit transducer, withselective processing at the receiving transducer or in the receivingelectronics.

[0264] The receive circuitry may be adaptive to variations in thephysical characteristics of the sensor subsystems. For example, EloTouchSystem controller product E281-2310 adapts to sensor subsystems ofvarying sizes by adjusting time windows used to gate received signals.

[0265] A multivariate analysis of different parameters may be employedto obtain further information from the received data. If more than onewave type is available, a controller may select an optimal wave or setof waves to analyze the sensed variable, i.e., under various conditions,a subset of the available information may be analyzed or employed indetermining the output.

[0266] In many embodiments, it is not necessary to capture phaseinformation contained in the received signals. However, in someinstances, it may be advantageous, or even essential to do so. Asdiscussed below, use of phase information allows generalization to casesin which a desired signal is coherently superposed on another desiredsignal or a parasitic signal. This novel feature of this invention isdiscussed in more detail below.

[0267] Phase and Separation of Superposed Signals

[0268] The phase information in received signals may be used todisentangle signals overlapping in time. With reference to FIG. 29(a),the effect of superposed waves is shown. In a phase sensitive receiversystem, a perturbation is detected at an i^(th) time slice if themagnitude of signal vector S₁ is significantly larger or smaller thanthe magnitude of the reference vector R₁, or if the relative phase shift

Δφ=φ₁−(φ_(1+Δ)+φ_(1−Δ))/2

[0269] is significantly non-zero, or some weighted combination of bothsuch as the quadratic sum of Δφ and |S₁−R₁|/|R₁| is greater than athreshold. In this formula, Δ is an integer comparable or larger thanthe number of time slices occupied by a typical touch perturbation. Notethat the value of Δφ, and hence the above conditions, are not affectedby global drifts in absolute phase, nor by global changes in the slopeof phase with time. Thus, a phase sensitive receiver system can reliablydetect a perturbation of a desired signal even in the presence of aninterfering signal. On the other hand, even if a significant change inthe signal phase at the i^(th) time slice occurs, this may be ignored byan AM detection system if |S₁|≈|R₁|.

[0270] This threshold need not be a global value, and may therefore varybetween different regions of the sensor. In theory, the threshold is setto reliably detect touches (low false negative rate) while preventingoutputs indicative of touch which do not correspond to a real touch (lowfalse positive rate). This may be optimized, for example, by determininga noise or signal instability level in a given region, and setting thethreshold above an average noise or instability level for that region.The threshold may be redetermined periodically, continuously, and/orbased on the occurrence of an event. While possibly more pertinent for aphase sensitive controller, a regionally determined threshold system mayalso be applied to traditional AM detector systems. The regions maycorrespond to the time dimension of a received signal, a physicalcoordinate of the sensor system, or other convenient space. Thethreshold determination may occur before, after or in conjunction with alogical analysis of the signal(s).

[0271] In a phase sensitive system, to ensure the perturbation islocalized as expected for a touch, a further analysis may be conducted,requiring the following conditions on the signal amplitudes for the timeslices a suitably small number of steps, Δ, away from the i^(th) timeslice.

[0272] φ_(1+Δ)≈φ_(1−Δ) |S_(1+Δ)|≈|R_(1+Δ)| |S_(1−Δ)≈|R_(1−Δ)|

[0273] Further refinements and elaborations of these basicphase-algorithm principles can be supported by modern electronics. Forexample, a DSP filter design may be provided, having adaptivecapabilities, i.e., it may learn new compensation strategies or detailsand apply these as necessary. It is noted that DSP functionality may beimplemented as a dedicated semiconductor design, e.g., a DSP or digitalfilter, or may be provided as software controlled functionality of ageneral purpose processor. Suitable DSP devices include TMS320C2x, C3Xor C5X devices from Texas Instruments, MC56000 series DSPs fromMotorola, Z8 series microcontrollers including DSP capability fromZilog, etc. DSP functionality may also he obtained through applicationspecific integrated circuits, programmable logic devices, and othertypes of semiconductor devices.

[0274] The acoustic signal propagation time for is very short ascompared to human reaction times. Therefore, the signal need not befully processed in real time. Typically it is sufficient to simplycapture and digitize a wave-form information as it is received. Thecaptured raw data can be processed later. It is possible to sequentiallyexcite a plurality of sensor subsystems and process of signal data fromone subsystem while another is excited. Thus, where a control system isprovided which may analyze the received signals, the substrate isavailable for additional measurement cycles, allowing various wave modeexcitation cycles to be analyzed independently. Under circumstanceswhere a high speed of data acquisition is desired, or computationalpower is available for this purpose, multiple sensor subsystems may alsobe analyzed in parallel.

[0275] D(i). AM Detection

[0276] For embodiments in which signal amplitude information issufficient to reconstruct touch positions, an AM (amplitude modulation)detection circuitry may be used. This is likely to be the case ifinterference from parasitic acoustic paths is negligible and if there isnever simultaneous receipt of more than one desired signal, from morethan one sensor subsystem, at a receiving transducer. Prior art acoustictouch systems assume a requirement the received signals can besuccessfully processed via AM detection. For the present invention, thisis not a requirement, but will nevertheless be true for manyembodiments. A typical AM detection circuit is shown in FIG. 30.

[0277] AM detection methods have been widely used in the prior art.Thus, AM receivers are disclosed in U.S. Pat. Nos. 5,162,618, 5,072,427,5,177,327, 5,243,148 and 5,329,070, expressly incorporated herein byreference and in U.S. Pat. Nos. 4,642,423, 4,700,176, 4,644,100 and Re.33,151, expressly incorporated herein by reference, which may beemployed, as applicable, with sensor embodiments. Controllers foracoustic touch panels are also disclosed in U.S. Pat. Nos. 5,380,959,and 5,334,805, expressly incorporated herein by reference.

[0278] The following AM detection scheme is typical of presentcommercial controller products. After a pre-amplifier stage, one foreach receive transducer, the received signal is multiplexed to, e.g. anMC1350 RF automatic gain controlled amplifier. The signal is thendetected, by for example a full or half wave rectifier circuit, asynchronous rectifier or an MC1330 detector. The detector is generallyfollowed by a single pole low pass filter. Bandwidth limiting is appliedat various stages of the signal chain. The resulting bandwidth istypically less than 0.5 MHz. The rectified signal, smoothed due tobandwidth limiting, is then buffered and digitized by an 8 or 12 bitanalog-digital converter. One digitized sample per microsecond istypical. The digitized data may be analyzed in real time and/or bufferedfor later analysis.

[0279] Prior art approaches to AM detection of touchscreen signals arenot the only AM detection techniques available. For example, thereceiver circuit may include a tuned narrow band AM superheterodynereceiver. The received signal, with a known transmission frequency, isinitially amplified in a low noise, high gain video-type amplifier. Theamplified carrier and signal is then mixed with an AFC (automaticfrequency control) tuning signal to achieve an IF of, for example, 3.54MHz. The narrow band IF (intermediate frequency) signal is filtered toeliminate other frequencies but retain amplitude information having abandwidth of less than 500 kHz, and then amplified. The amplified,filtered IF signal is then detected by a full wave rectification andfiltering or synchronous detection. The AM detected signal is digitized.

[0280] For many embodiments of the present invention, the low-levelrecognition of signal perturbations may proceed via known AM detectionschemes, while the higher-level logical analysis of identified signalperturbations differ from known systems, as described herein.

[0281] A variation of AM detection methods disclosed in U.S. Pat. Nos.5,380,959, and 5,334,805, in which distinct X and Y receive transducersgenerate signals. One receiver responds to the desired signal plusinterference from acoustic parasitic paths or electromagneticbackgrounds, and the other responds only to the interference. Whileperhaps atypical, there may be cases in which the interference isreceived with the same phase and amplitude for both the X and Y receivetransducers. In such cases the interference-only signal may becoherently subtracted from the other signal, and the resultinginterference-canceled signal processed via standard AM detectionmethods. This combining of signals from two receive transducers is verydifferent from the phase-sensitive detection methods described below, inwhich a controller can process input from a single receive transducereven if multiple signals are superposed; the apparent purpose of thedual receiving transducer circuit of U.S. Pat. Nos. 5,380,959 and5,334,805 is to avoid the need to for processing of signals overlappingin time that would otherwise interfere with AM detection schemes.

[0282] As shown in FIG. 30, a pair of transducers, X and Y, provideinputs to band pass filters 3001 and 3002. These band pass filters mayalso be notch filters, and indeed the preamplifiers 3003, 3004 are bandlimiting. The outputs of the preamplifiers 3003, 3004 are multiplexedthrough multiplexer 3005, depending on which transducer is activelyreceiving signal. A further bandpass filter 3006 may be provided. Avoltage controlled amplifier 3007 is provided to allow a controller toadjust the gain of the input channel. A band pass filter 3008 eliminatesDC and low frequency components, as well as high frequency noise, andthe amplitude of the signal is detected in a full wave rectifier 3009 orRMS circuit. The detected output is then again filtered with a low passfilter 3010, amplified with amplifier 3011, and output. The output maybe fed, for example, to a sample and hold amplifier and analog todigital converter (not shown).

[0283] D(ii). Phase Sensitive Detection

[0284] According to one set of embodiments according to the presentinvention, two (or more) sets of wave paths are superposed and portionsare received simultaneously at the receiver. This scenario isdemonstrated in FIG. 9D(i). A superposed set of wave paths maycorrespond to a desired sensor subsystem, or be due to parasiticacoustic paths. No presumption is made that there is any particularabsolute phase relationship between the various sets of superposed wavepaths, furthermore the phase relationships between superposed signalsmay drift with time.

[0285] Four representative relative phase states of two waves are: inphase, out of phase, leading and lagging. For example, waves havingequal amplitude pass through a portion of a substrate subject to a touchinduced perturbation, where, for illustrative purposes, we assume afinger touch completely absorbs one of the waves. If the waves are inphase, the touch will result in a factor of two reduction in totalamplitude. If the waves have leading and lagging phase relationship of90°, the finger touch results in only a 29% reduction in the magnitudeof the net signal amplitude. If the waves are out of phase (180° apart),the net amplitude will be zero before the touch, and a finite signalwill appear due to the finger touch. Such effects confuse typical touchrecognition algorithms based on AM detection schemes, and hence is whyit has been heretofore been considered unacceptable for sensor design toallow signal amplitudes to combine in such a fashion.

[0286] As shown in FIG. 9D(1), two signals, each bearing touchinformation, are present simultaneously. When summed, there are a numberof possibilities, as discussed above FIG. 9D(2) shows a phase coherentsuperposition, wherein the amplitudes of the two waves are additive. Ina phase coherent detection scheme, as shown in FIG. 9D(3), the secondwaveform 21 is subtracted from the first waveform 20, with thepossibility of negative amplitudes 22, and an increase in signalamplitude corresponding to a wave perturbation 23. FIG. 9D(4) shows adestructive interference of the two waves, with RMS detection of theresulting waveform, so that negative amplitudes are not possible. Moregenerally, the phase relationship between the two signals in FIG. 9D(1)may drift while they are being received, thus leading to signals thatare even more problematic for AM detection schemes.

[0287] Embodiments in which the controller captures phase as well asamplitude information can utilize such superposed signals. For example,as noted in FIG. 29(a), signal perturbations due to touches may berecognized by a displacement of the net amplitude in two-dimensional I-Qspace. This is true even if the magnitude of the net signal does notchange. Even in the presence of superposed signals, acoustic attenuationof the desired signal will always change the net signal vector in I-Qspace. As noted in the discussion above regarding FIG. 29(a), it ispossible to implement algorithms that filter our various drifts in theglobal phases of the superposed sets of waves.

[0288] In cases where the drifts in the global phases of superposed setsof waves is slow compared to the time it takes the controller to updatethe reference I-Q amplitude vectors R₁, the presence of a touch may besimply recognized as a significantly non-zero value for |S_(i)−R_(i)|.

[0289] There are many ways to implement a phase-sensitive controller.One basic approach is to compare the phase of received signals with afree running reference clock signal, as shown in FIG. 31(c). Otherapproaches may make use of phase-locked loops, as shown in FIGS. 31(a),31(b), and 31(d).

[0290] In the context of FIG. 31(c), homodyne mixing provides aparticularly simple conceptual approach. For example, for a sensoroperating at 5 MHz, a continuous 5 MHz reference clock signal 3101 isgenerated. The tone burst to the transmit transducer has a fixed phaserelationship to this reference clock signal. An “In-phase” or “I” copyof a reference clock signal 3102, derived by time-shifting the clockwith phase shifter 3 103, as necessary, is mixed in mixer 3104 with afiltered signal 3106 from a receive transducer 3105, and the resultingmixed signal passed through a low-pass filter 3107 and then digitizedwith analog to digital converter 3108; thus an I wave-form 3109 iscaptured. A “Quadrature” or “Q” copy of the reference clock signal isgenerated with a 90° phase shift with respect to the I reference clocksignal, generated by quadrature generator 3110; this is similarly usedto capture the Q wave-form 3114 through a mixer 3111, low pass filter3112 and analog to digital converter 3113. In this fashion, S₁=(I₁,Q₁)is directly generated for use in the implementation of algorithms basedon FIG. 29(a). The digital processing may be accomplished with generalpurpose microprocessor, or more specialized digital signal processors,not shown in FIG. 31(c).

[0291] An alternate phase locked loop embodiment is shown in FIG. 31(a).In this figure, the transmit burst signal generator also controls thereceive clock generator. The transmit burst generator 3147 produces anoutput which is influenced by a model 3148, which is, for example, a setof delays and filters. This is then fed to the phase locked loop circuit3149. The remainder of FIG. 31(a) is similar to the circuit of FIG.31(b), discussed below.

[0292] In certain instances, it may be preferable to capture thereceived signal from the receive transducer 3122 with sufficient hightime resolution, e.g., four times the carrier frequency f₀, to capturethe RF waveform. The received signal is preferably filtered with anarrow band filter 3127. In this case, the sampling clock 3123 providesa phase reference, to operate a track and hold amplifier 3124 and analogto digital converter 3125, as shown in FIGS. 31(e) and 31(f). Inparticular, a system as shown in FIG. 31(e) provides the fullflexibility provided by programmable digital signal processing 3126. Forexample, in cases where two or more operating frequencies are used, aparticular received signal may be selected, in part, by loadingappropriate digital-signal-processing constants needed to produce afilter at the desired frequency selected the in software. FIG. 31(f)provides an application specific digital signal processing circuit 3120,which performs phase extraction, digital filtering, and decimation intime. Thus, the output data rate is reduced, and a typical microcomputer3121, without particular digital signal processing prowess, may be usedto perform further analysis.

[0293] In such a system that captures a RF wave-form, the receivedsignal is digitized directly at a rate in excess of the Nyquist rate,after preamplification and standard signal conditioning (which mayinclude narrow band filtering), and is then processed using a digitalsignal processor (DSP) 3126. In this case, the DSP 3126 may operate inreal time, or buffer the received digitized waveform in a RAM andprocess it with some latency. For example, with a 5.53 MHz excitation,and a 500 μS echo analysis, a RAM buffer on the order of about 16 kWordsmay be required, with samples acquired about every 40 nanoseconds (25Megasamples per second). Of course, this storage requirement may bereduced if the entire signal need not be fully analyzed at one time; forexample, the signal may be divided timewise, and blocks of consecutivesamples analyzed consecutively. This will focus the analysis on sectionsof the sensor for each excitation burst. The actual sample timing mayvary adaptively to track the received waveform or be at a constant rate.The digitized signal, after detection of the relevant parameters, maythen be digitally filtered (FIR, IIR, auto regression, or more complexfilters such as auto regression and moving average process filtering),waveform analyzed, adaptively compensated, compared to a reference, andsubject to other techniques to determine waveform perturbingcharacteristics of the touch, such as location, z-axis (pressure), andtype of object (wave mode absorption characteristics). Thus, aselective, sensitive system is provided.

[0294] The reference clock signal may be generated from the receivedsignal with a phase-locked loop 3130, as shown in FIG. 31(d). Typically,a phase locked loop 3130 may be implemented in hardware, so that anoscillating signal is generated which corresponds to a “carrier” wave ofanother signal. As shown in more detail in FIG. 31(b), the phase lockedloop 3131 tracks the signal, but is limited to vary more slowly by timedelays 3132. Thus, drift in phase due to manufacturing tolerances andenvironmental effects may be filtered, and yet any rapid changes inphase due to a touch may be determined by comparing the generatedcarrier with the actual signal, or by analyzing the error signal. Alsoshown in FIG. 31(b) is a pair of mixers 3133, 3134, for mixing the inphase and quadrature synthesized clock outputs 3135 with the receivedsignal, and a pair of RMS detectors 3136, 3137 to detect each phasesignal. As shown, the circuit seeks to maximize the difference betweenthe RMS value of the I and Q signals, to shift the phase of the VCO 3138when a relative change occurs in the respective amplitudes. The VCO 3138has a lock input 3139 from the controller 3140 to prevent compensatorychanges, for example where a touch is detected. The RMS values of the Iand Q signals are multiplexed in multiplexer 3141, and digitized inanalog to digital converter 3142, and input to the controller 3140. Thecontroller 3140 has associated RAM 3143, for storing transient data, andROM 3144, for storing programs and tables, as well as input and outputdrivers 3145. As shown in FIG. 31(d), the detection circuit 3146 maygenerate the I and Q signals, which are multiplexed and digitized,without RMS processing.

[0295] If the control feedback of a phased-locked loop is sufficientfast, then, for example, the voltage controlling a variable-frequencyoscillator within the phased-locked loop may be integrated and digitizedto directly provide a measure of signal phase. With a DC-reject filter,variations in the global phase offsets can be eliminated. Combined withAM detection, this provides digitized I-Q signal amplitudes in polarcoordinates. Thus phase-sensitive controllers may digitize signals inI-Q space in either Cartesian or polar coordinates.

[0296] The electronics industry provides, and can be expected tocontinue to introduce, components that enable fabrication ofphase-sensitive controllers. For example, impressive digital signalprocessing power can be provided by an Intel Pentium processor or aTexas Instruments TMS 320C80 DSP coprocessor. Rapid digitization ofsignals is possible at 40 MSPS from one or more Texas InstrumentsTLC5540INSLE 8-bit ADCs, or at 10-bit resolution at 20 MSPS from one ormore Analog Devices ADS820 10 bit ADCs. Suitable PLLs are, for example,the Signetics NE/SE564, NE568, (or equivalents) and Texas InstrumentsTLC2932 (or equivalent). Suitable mixers include the NE/SA602 and NE612(or equivalent), which each include a double-balanced mixer circuit.See, Signetics NE/SA602 data sheet and Signetics AN1981 and AD1982. Thecost-performance trade-offs for particular applications will determinethe most suitable choice of components for phase-sensitive controllers.

[0297] Use of intermediate frequencies (“IF”) with heterodyne mixing maybe considered as a means to shift received signals to a frequency whichis a standard for a mass-market signal processing application. Forexample 455 kHz and 10.7 MHz are standard IF frequencies for radio andvideo communication. Further, where a plurality of frequencies are to bereceived, a heterodyne receiver allows a common filter and receiver tobe employed for receiving the various signals after tuning. Note that itis possible for the intermediate frequency to be higher than theoperating frequency for the touchscreens. The use of IF frequenciesfurther increases options for electronic components to be used asbuilding blocks of a phase-sensitive controller.

[0298] E. Intermediate Level Processing

[0299] The purpose of intermediate level processing is to efficientlyreconstruct delay-times, and perhaps quantitative absorptioninformation, for perturbations of the signals due to touches, and to doso with sufficient immunity to signal artifacts due to temperature,humidity, electronic emissions, radio frequency interference, and thelike. Intermediate-level processing need not be fool-proof, as higherorder processing within the algorithm may also reject artifacts. Iffact, intermediate level processing can be optimized for efficiency atthe expense of immunity if the higher level algorithms requireconsistent and redundant information from three or more sensorsubsystems.

[0300] Typically, the relevant touch information is contained within arelatively narrow bandwidth about the nominal operating frequency orfrequencies. Many artifacts can be eliminated with appropriate frequencyfiltering, either in hardware or via digital signal processing.

[0301] Touch perturbations occur on a fast time scale relative to manysources of signal drift. Therefore, as is typical of the prior art, anadaptive baseline is used to distinguish genuine touch information fromsystematic drifts in signal amplitudes. Note, however, in contrast toprior art, the adaptive baseline need not be limited to AM amplitudeinformation; the adaptive baseline may also incorporate phaseinformation.

[0302] As discussed above, the baseline and/or threshold processing maybe regionally varying, and may be optimized for highest performance.

[0303] In the context of a phase-sensitive controller, use of anadaptive baseline is conceptually similar to known AM systems. Thus, forexample, an adaptive baseline correction is implemented by memorizing abaseline pattern and analyzing the received signal with respect to thememorized baseline to determine the presence of a perturbation. Thereference condition compensates for long term and environmentalconditions, and facilitates meaningful analysis of the received signals.The reference condition is preferably derived periodically in theabsence of a touch or other indications of transient conditions.Furthermore, the baseline may also be updated continuously based onportions of the signal presumed to be unaffected by transientconditions, even during periods when a touch occurs. The referencesignal therefore compensates for many physical characteristics of thescreen, contamination, as well as long term drift due to, e.g.,temperature. Known systems implement such adaptive baselines.

[0304] Embodiments of the present invention using phase sensitivecontrollers necessarily involve more than simple subtraction of abaseline. The baseline information, e.g. a memorized referencewave-form, contains phase as well as amplitude information. Optionally,stability or noise information may be stored. Simple subtraction ofreference amplitudes is replaced by mathematical processing involvingcalculations of displacements in I-Q space.

[0305] Whether or not the controller is phase sensitive, the receivedsignals are processed to provide time-delays and magnitudes of candidatetouch perturbations for the sensor subsystems. This information is thenused in the next level of data processing.

[0306] In cases where there is an ambiguity regarding which sensorsubsystem corresponds to a candidate touch perturbation, allinterpretations may be provided to the higher level algorithms forfurther processing. Such ambiguities occur in sensor systems as shown inFIGS. 19, 22(c), and 28. A case in point is where a phase-sensitivecontroller simultaneously receives signals from two sensor subsystemsthrough a common receive transducer, and the controller may not have adirect means to determine which of the coherently summed signals hasbeen perturbed.

[0307] F. Analysis of Perturbations

[0308] Candidate touch perturbations are analyzed to reconstructpositions of touches. Optionally, the touch system may output furtherinformation regarding touches such as the touch “pressure”, i.e.magnitude of acoustic absorption, and “water-rejection” touchcharacteristics such as the ratio of shear-wave to Rayleigh-waveabsorption. Furthermore, the present invention supports algorithms withincreased tolerance for shadowing due to contaminants, with unambiguousmultiple-touch capability, and with enhanced reliability due toconsistency checks based on redundant measurements.

[0309] Generalize to Non-Orthogonal Sensor Subsystems

[0310] Although the scope of this invention includes schemes whichoutput but a single coordinate, the primary objective of most touchsystems is to output two-dimensional coordinates of touches on asurface. If a touch is sensed by two or more sensor subsystems, thenthere is typically a unique touch position on the touch surface that canaccount for the resulting delay times for the perturbations observed inthe corresponding signals. Note that coordinates measured by thesubsystems according to the present invention need not correspond to anoutput coordinate axis and need not be orthogonal to each other, thearrays, nor the edges of the glass. Thus, where the sensing waves do notcross the touch sensitive region of the substrate orthogonal to areference coordinate system, the controller performs a coordinatetransformation on one or more received signals to the desired coordinatesystem. The coordinate transformation to the output system may occurbefore or after the two-dimensional position of the touch isreconstructed.

[0311] Where more information is received than is required forreconstruction of the touch position, e.g., three received signals fortwo coordinate axes, a consistency checking and optimization analysismay be executed to make optimal use of the available information. Aweighted average may be constructed based on coordinates determined bypairs of sensor subsystems sensing the touch. Alternately, the algorithmmay use the coordinate determined by the sensor-subsystem pair mostlikely to provide reliable and accurate coordinate measurements.

[0312] Once a touch is registered, the coordinates of the touch aredetermined by calculating a center of a touch, possibly with correctionfor non-linearity or scaling, and output as the touch position.

[0313] There is no requirement here that there is a linear, orapproximately linear relationship between delay times of touchperturbations and any coordinate of interest.

[0314] Dual Mode Sensing of Touch Characteristic

[0315] As with prior art sensors, a “pressure” or “Z axis” value for thetouch may be included with the touch position as part of the output fromthe touch system. Additional information may be provided by the presentinvention in cases where a touch is sensed by more than one acousticmode. See FIG. 26. For example, if a touch is sensed by both ahorizontally polarized shear wave and an acoustic mode subject toleaky-wave-radiation damping into water contaminants, such as a Rayleighwave, then the ratio of shear-wave to non-shear-wave acoustic absorptionprovides an touch characteristic that may be used for water rejection. Athreshold may be defined so that “touches” due to water drops arerejected while finger touches are accepted. This in an important featureof sensors utilizing more than one acoustic mode in the touch region.Thus, according to FIG. 26, a touch position is reconstructed 2601. Themagnitude of the signal perturbation for each wave is determined 2602.The consistency of the perturbation is tested with respect to knownconditions 2603, to allow classification of the characteristic of thetouch.

[0316] Anti-Shadowing

[0317] For sensor designs in which touches are designed to be sensedwith three or more sensor subsystems, anti-shadowing algorithms arepossible. See, FIGS. 25(a) and 25(b). Shadowing occurs when acontaminant or other acoustic obstruction so reduces signal amplitudesso as to produce an unresponsive dead region. For a sensor subsystem,the dead region includes not only the location of the contaminant, butalso the entire length of the acoustic paths shadowed by thecontaminant. For example, in rectangular sensors according to the priorart with X and Y sensor subsystems, a strongly absorbing contaminant oneinch in diameter will result in a cross-shaped dead region, with oneinch horizontal and vertical stripes intersecting at the contaminant,within which two-dimensional touch coordinates cannot be reconstructed.Note that the loss of either coordinate measurement results in aninability to reconstruct a touch position. In contrast, when a touch iswithin the sensitive zone of three or more sensor subsystems, atwo-dimensional position can still be determined if one coordinate islost in the shadow of a contaminant.

[0318]FIG. 25(a) shows a simplified flow chart for an anti-shadowingalgorithm. The algorithm flow chart is abbreviated and representative,setting forth the basic steps. Application of the basic concepts herewill be considered below in the context of specific embodiments of theinvention. All significant perturbations in all sensor subsystem signalsare identified 2501. The delay times are determined for each signalperturbation 2502. Perturbations in overlapping regions of sensorsubsystems are matched 2503. Finally, from the matched sets, touchpositions are calculated 2504. It is noted that the shadowing influencewill be considered a strongly absorptive, slowly changing perturbation,in contrast to a touch, which is generally of short duration and may beless than completely absorptive. FIG. 25(b) shows an antishadowingalgorithm in more detail for an X, Y, 30° diagonal path sensor system asshown in FIG. 13. The X signal is searched for a touch 2511. If found,2512, the Y signal is searched, or if not found, the Y signal is alsosearched 2521. If X and Y are found, the touch position is reported2513. The diagonal paths of the two triangular sensor subsystems arethen searched for touch, 2514, 1517, and if found, the missing Y iscalculated 2515, 2518, and reported 2516, 2519. If no diagonal touchperturbation is found, the X touch information is likely artifact andignored 2520. If no X is found, the Y is searched for a touch 2521. Ifboth X and Y fail to show a touch, it is presumed that no touch ispresent 2522. On the other hand, if a Y touch is found, the diagonalpaths are then searched for touch 2523, 2526, and if found, the missingX calculated 2524, 2527, and reported 2525, 2528. If no diagonal touchperturbation is found, the Y touch information is likely artifact andignored 2529.

[0319] For a shadowing contaminant, particularly one which is observedby three or more sensor subsystems, the controller has information fromwhich one can determine the presence and location of the contaminant.Such information can also be used to provide user feedback to remedy theproblem. For example, diagnostic software may include a maintenanceoption in which “Clean me here!” messages appear as needed with arrowsand targets.

[0320] Multiple Touch Capability

[0321] A particular aspect of certain embodiments of the presentinvention is the ability to detect and analyze multiple simultaneoustouches, based on the plurality of waves. See FIGS. 24(a) and 24(b).

[0322] Prior art sensors are subject to the following ambiguity whensimultaneously subjected to two or more touches. Consider an acoustictouchscreen is subjected to two touches, one may be represented withcoordinates (X₁, Y₁) and the other with coordinates (X₂, Y₂). Thereceived signal providing X coordinate information contains two signalperturbations allowing the determination of the values of X₁ and X₂. SeeFIG. 9B. Likewise the Y signal allows reconstruction of the values of Y₁and Y₂. The signals make it clear that there are two touches. However,there is an ambiguity whether the two touches are at coordinates (X₁,Y₁) and (X₂, Y₂), or alternatively at coordinates (X₁, Y₂) and (X₂, Y₁).The ambiguity concerns which X coordinate to pair up with which Ycoordinate. With increased complexity, similar ambiguities are presentfor three or more simultaneous touches.

[0323] To some extent, this ambiguity can be resolved by timing andquantitative attenuation information. If the (X₁, Y₁) touch makescontact with the sensor before the (X₂, Y₂) touch, the controller maydecide that a (X₁, Y₁)/(X₂, Y₂) double touch is more likely to follow a(X₁, Y₁) single touch than a (X₁, Y₂)/(X₂, Y₁) double touch. Similarly,touch amplitude information may be used. Assume, for example, that thesecond touch is a lighter touch, i.e. with less attenuation, than thetouch at (X₁, Y₁), being represented using lower case letters for itstouch coordinates (x₂,y₂). By matching amplitudes, the controller maydecide that a (X₁, Y₁)/(x₂,x₂) double touch is more likely than a(X₁,y₂)/(x₂, Y₁) double touch. In many cases, these methods will resolvethe ambiguity. However, by themselves, these methods are not alwaysreliable. Two touches may have approximately the same attenuation ormake contact simultaneously. Most importantly, if X₁ and X₂, or Y₁ andY₂, are sufficiently close in value, the corresponding perturbations inthe signal will overlap and make it problematic to reliably andaccurately disentangle the two coordinate values.

[0324] Here, it is advantageous to cover desired touch regions withthree or more sensor subsystems, as shown in FIGS. 13 and 14. FIG. 24(b)presents an algorithm that may be used with the sensor in FIG. 13. Usinga pair of sensor subsystems, candidate touch positions, subject toambiguities, may be determined 2401X, 2401Y. For each candidate touchposition, delay times can be predicted for the remaining sensorsubsystem(s). For the valid touch positions, the predicted delay timeswill correspond to measured touch perturbations along all axes. Moregenerally, a valid touch is recognized by a self-consistent triple(s) ofdelay times from three or more sensor subsystems. From theseself-consistent triples, the touch positions may be calculated.

[0325] The comparison process includes testing candidate touch positionswith the various possibilities. Thus, the candidates are identified2405, the predicted perturbations calculated for each candidate touchposition for the diagonal axes 2406, 2408, and the predictedperturbation compared with the actual perturbation for each diagonalaxis 2407, 2409. The consistent candidates are determined for the touchpositions and output 2410. The candidates are evaluated successively2411.

[0326] Also note that the touch perturbation interference problem notedhere is a variant of the “contaminant” shadowing problem, and hence maybe solved with the aid of anti-shadowing algorithms. Namely, thealgorithm may base touch position determination on sensor subsystem datafor which touch perturbations are well separated.

[0327] A multiple-touch algorithm may be subject to the burden ofsorting through a relatively large number of candidate touch positionsdue to the nature of combinatorics. However, unless the number ofsimultaneous touches becomes excessive, this is not a significantproblem for algorithm response times. A substantial amount of datareduction occurs in the low level control, i.e., the data stream fromthe analog to digital converter is reduced to a relatively small set ofparameters, e.g., a timing, width and amplitude of each detectedperturbation. Because the amount of data to be processed by the highlevel control, i.e., logical analysis, is relatively small, acomprehensive analysis is possible. Therefore, if three perturbationsare detected in each of three sets of waves, a logical analysis of eachof the 27 possible coordinate locations of three touches is possible.Therefore, the perturbation characteristic, attenuation and timingcorrelation of each perturbation may be compared to predict a mostlikely set of points. If one of the perturbations, for example,comprises artifact or interference, the corresponding coordinate may beexcluded or ignored.

[0328] It is also noted that, in order to define a touch position fromamong a number of possibilities, the resolution of ambiguity need not beperformed strictly by acoustic means. For example, a coarse infraredtouch detection grid (rotated with respect to coordinates measured byacoustic sensor subsystems) may be used to detect the gross position ofone or more touches, with the coarse position used to consistentlydetermine the exact location of multiple perturbations in the receivedacoustic wave signals.

[0329] Redundant Measurement Consistency Checks

[0330] Even when there are not discrete ambiguities due to multipletouches, algorithms based on self consistency of redundant coordinatemeasurements provides a means to eliminate artifacts. See FIG. 24(a).The use of self-consistent triples of delay times from three or moresensor subsystems goes beyond the redundancy checks used in the priorart.

[0331] According to known schemes, waves travel along axes whichcorrespond to a pair of perpendicular physical edges or major axes of asubstrate, and one set of waves senses touch along each axis. Thus, asingle touch will produce a pair of corresponding perturbations in eachof the sets of waves, which directly correspond to the coordinate systemof the substrate. Thus, when a touch is detected, the analysisdetermines the position along each of the axes and outputs a coordinatepair. This known system thus redundantly detects the presence of atouch, that is the presence of a touch is validated if it is observed inboth the X and Y channels. Thus, uncorrelated noise which effects onereading may be ignored if it does not effect a subsequent reading on theother axis. Further, a minimum perturbation duration may be required, sothat at least one confirming reading may be required in order for atouch to register. However, known systems do not include a higher levelof redundancy.

[0332] The present invention, encompasses the analysis of redundancy,such that a position along one coordinate axis is determined usinginformation which provides at least two wavepaths through a touchposition to determine a position along a single axis, or two waveshaving differential absorptivity characteristics for a touch passingthrough the touch position. According to another aspect of theinvention, a coordinate transform is performed to translate signalsproduced by transducers from the various wavepaths to a desiredcoordinate system, wherein the transform requires at least two wavepathsto define a single output coordinate.

[0333] The perturbation analysis may thus also include validity checkingand position estimation based on the multiple signals, wherein aninconsistency may be present. Thus, the signals are logically analyzedaccording to rules, which may be predetermined or adaptive, to define anoutput which should be produced for a given set of inputs.

[0334]FIG. 24 shows a multiple-touch/redundancy-check algorithm flowchart for a touch sensor having two orthogonal sets of acoustic pathsand a non-orthogonal set of acoustic paths. The algorithm flow chart isabbreviated and representative, setting forth the basic steps.Significant perturbations in all sensor subsystem signals are identified2401. The delay times for all perturbations is determined 2402. Selfconsistency of triples is then evaluated, with errors evaluated forsignificance 2403. The touch position(s) is then calculated 2404 andoutput. Application of the basic concepts here will be considered belowin the context of specific embodiments of the invention. Such analgorithm is able to resolve multiple-touch ambiguities, and providesfor additional noise rejection, allowing operation with a lighter touchthreshold and/or operation in a noisier environment.

[0335] Where supposedly redundant information is inconsistent, thesignals may be analyzed to determine if one of the signals is likelyinaccurate or in error, and a most likely coordinate output. Further,where an inaccuracy or error follows a pattern, for example indicativeof poorly optimized calibration constants used to correlate delay timeswith touch positions, an error signal may be provided which ultimatelyprompts a user to remedy the problem, e.g. re-run calibration software.

[0336] Wave Modes

[0337] As noted earlier, this document defines “surface acoustic waves”(hereinafter “SAW”) as acoustic waves for which a touch on the surfaceleads to a measurable attenuation of acoustic energy. Surface acousticwaves are used for the segments of acoustic paths traversing the desiredtouch sensitive zone of sensor subsystems. Other segments of theacoustic paths, e.g. along the arrays to and from the transducers, canuse any acoustic modes that couple to transducers and also couple to thedesired surface acoustic wave via scattering by the reflective array.Several examples of surface acoustic waves are known.

[0338] There are many advantages to Rayleigh waves including high touchsensitivity and high power density at the touch surface even forarbitrarily thick substrates. Rayleigh waves maintain a useful powerdensity at the touch surface due to boundary conditions that allows thesubstrate material to deform into free space, effectively reducingmaterial stiffness for the wave and hence its velocity, thus resultingin a reduced-velocity wave guiding effect near the surface. For example,this enables Rayleigh waves to be used on a CRT faceplate whichrepresents a very thick substrate relative to the acoustic wavelengths.

[0339] Like Rayleigh waves, Love waves are “surface-bound waves”.Particle motion is vertical and longitudinal for Rayleigh waves; bothshear and pressure/tension stresses are associated with Rayleigh waves.In contrast, for Love waves, particle motion is horizontal, i.e.parallel to the substrate surface. Only shear stress is associated witha Love wave. Love waves have the advantage that they do not couple towater or other liquid or quasi-liquid contaminants, e.g. a siliconerubber seal, via pressure-wave radiation damping. Of course, eliminationof radiation damping will also reduce sensitivity for a finger touchwhich must now rely on viscous damping alone. However, for market nichesfor which liquid contamination is a particular problem, a Love wave maybe preferable to a Rayleigh wave. Depending on substrate design, theconcentration of acoustic power at the surface, and hence the touchsensitivity, can be varied. A key advantage of Love waves, or moregenerally asymmetric horizontally polarized shear waves, is that theymay have no appreciable energy on the lower surface of the substrate.

[0340] Another class of surface acoustic waves of possible interest inconnection with acoustic touchscreens are plate waves. Unlikesurface-bound waves, plate waves require the confining effects of boththe top and bottom surfaces of the substrate to maintain a useful powerdensity at the touch surface. Examples of plate waves include symmetricand anti-symmetric Lamb waves, zeroth order horizontally polarized shear(ZOHPS) waves, and higher order horizontally polarized shear (HOHPS)waves.

[0341] Use of plate waves constrains the thickness of the substrate. Forplate waves, the touch sensitivity decreases with increasing platethickness. For low-order plate waves such as ZOHPS waves, phase velocitydifferences with respect to neighboring acoustic modes (i.e. n=1 HOHPSfor ZOHPS) shrink with increasing substrate thickness making cleanseparation of modes more difficult. ZOHPS sensors operating at 5 MHz arethus typically limited to substrate thickness of about one millimeterfor glass. Higher order modes can be used with somewhat thicker glasssubstrates of 2 to 3 millimeters, in part because of a largerphase-velocity differences from neighboring modes, and in part becausenodal planes inside the substrate help concentrate acoustic power at thetouch surface. Note that plate waves are equally sensitive on the topand bottom of the substrate. For applications in which limitations onsubstrate thickness are not a problem, and for which bottom-side touchsensitivity is not a problem, plate waves are viable options.

[0342] The choice of acoustic mode effects touch sensitivity, therelative touch sensitivity between water drops and finger touches, aswell as a number of sensor design details. However, the basic principlesof acoustic touchscreen operation are largely independent of the choiceof acoustic mode.

[0343] As noted above, there can be particular advantages tosimultaneous detection of touches with more than one acoustic mode. Forexample, a water rejection can be based on a comparison of touchperturbations from a horizontally polarized shear mode (e.g. Love,ZOHPS, HOHPS) and from a mode that is damped by pressure-wave radiationin liquids (e.g. Rayleigh, Lamb).

[0344] Mode Distinguishing Physical Filters

[0345] Sensor subsystems are designed for a particular set of acousticpaths and acoustic modes. Ideally, the receiver signal is entirely dueto the desired paths and modes. With the aid of a phase sensitivecontroller, some interference from parasitic acoustic signals may beacceptable, nevertheless it is still desirable to avoid excessiveparasitic interference. Various physical filters may be employed toassure that sufficient suppression of parasitic modes is achieved.

[0346] The transducers and arrays provide the most basic filters tosuppress undesired acoustic modes. For example, a Rayleigh-wavetransducer composed of a pressure-mode piezoelectric element and a wedgewill couple strongly to Rayleigh waves but very weakly to possibleparasitic horizontally-polarized shear waves. The arrays themselves aretypically very selective mode filters. Referring to FIG. 11, an array'sspacing vector is designed to efficiently scatter the desired mode inthe desired direction; fortuitous circumstances are required for thearray to coherently scatter the wrong mode or the right mode in thewrong direction. In addition to these two fundamental mode filteringmechanisms that are inherently part of the sensor design, further modefilters may be introduced.

[0347] In some cases, the mode selectivity of reflective arrays can beenhanced by means of the depth structure of the reflective arrays. Forexample, FIGS. 5A and 5B of U.S. Pat. No. 5,072,427 consider reflectivematerials on both the top and bottom surfaces of a substrate in order toreduce parasitic mode generation during mode conversion from a ZOHPSwave to a Lamb wave of a specified symmetry (symmetric oranti-symmetric). In principle, optimal reflective array mode selectivitycould be obtained if one had full design control over the depth profileof the reflector structure; this is not always cost-effective inpractice.

[0348] Commercial acoustic touchscreens typically use acoustic dampingmaterials to absorb or “filter out” undesired acoustic paths. Forexample, in sensor designs for which the substrate edges serve nodesired acoustic purpose, acoustic absorbers such as contact adhesivesare placed around at least part of the perimeter of the substrate toeliminate possible reflections off the edge of the glass. Such absorbersat the substrate perimeter are analogous in function to thewave-absorbing design of the sides of Olympic-style swimming pools;waves impinging the perimeter are not reflected back into the activearea where they may complicate signal analysis or slow down swimmers.Such prior art techniques may also be applied to embodiments of thepresent invention.

[0349]FIG. 14, reference numeral 52, of U.S. Pat. No. 5,177,327 alsoshows use of acoustically absorbing materials to differentially absorbdesired and parasitic modes. Such techniques may also be applicable toembodiments of the current invention. Reverse reflection schemes, suchat that shown in FIG. 17 of U.S. Pat. No. 5,177,327, increaseopportunities to place mode filters in the acoustic path from thetransmit to receive transducers.

[0350] The substrate itself may be designed to selectively propagatedesired modes and cut-off or absorb undesired modes. For example, if thedesired mode is a lowest order plate wave, e.g. a ZOHPS or a flexuralwave, then a sufficiently thin substrate will not support Rayleigh wavesnor the higher order plate waves for which the cut-off frequency isabove the operating frequency; the thinning may be in a limited regionor for the entire substrate. As another example, the glass-polymer-glasslamination of safety glass may serve as a Rayleigh-wave substrate forwavelengths sufficiently small compared to upper glass thickness; allplate wave modes will be absorbed by the acoustically absorbing adhesivebonding layer. As yet another example, a Love-wave substrate may bedesigned with a thin slow-velocity layer on the top, a higher velocitymedium in the middle, and an acoustically absorbing material on thebottom. The thickness of the slow-velocity layer can be reduced untilonly the lowest-order Love wave is captured. Such a Love-wave substratewill support the lowest-order Love wave and a modified Rayleigh wave,but will not propagate any of the (modified) plate-wave modes.

[0351] Some embodiments involve reflective boundaries. In some cases,the reflective boundary may be a source of parasitic mode conversions,for example when the reflective boundary is simply a machined edge ofthe substrate. In other cases, the reflective boundary may providefurther mode filtering, for example reflective boundaries based oncoherent scattering off of multiple reflectors, i.e. reflectiveboundaries based on the principles of FIGS. 11 and 17.

[0352] One interesting variant of a reflective boundary is a bevelededge of a substrate. As the substrate thins, cut-off frequencies forhigher order plate-wave modes increase. If the beveled edge becomessufficiently thin to drive a cut-off frequency above the operatingfrequency, then the corresponding mode will be reflected. Due to thehigh acoustic power density at the reflection point (analogous to thelong dwell time at the maximum elevation of an object rolling up ahill), an absorber placed at the reflection point will have increaseddamping effect. For a beveled substrate edge, different higher ordermodes will have reflection points at different distances from thesubstrate edge; thus allowing strategically placed absorbers todifferentially absorb different modes. This basic mode-filteringtechnical applies to both Lamb waves and horizontally polarized shearwaves.

[0353] As an example, let us look at horizontally polarized shear wavesin more detail. A mode selective filter may be provided by a substratehaving a beveled reflective edge. As the substrate becomes thinner, thecutoff frequencies for HOHPS modes increase. As the wave-guide cut offfrequency increases, the group velocity decreases. When the substrate isthin enough for the cut-off frequency to equal the operating frequency,the group velocity becomes zero and the wave is reflected. Thisreflection point differs for differing wave modes, such that the largerthe order n of the mode, the further from the edge of the substrate willbe the reflection point. An acoustic wave generally has enhancedsensitivity to absorbing materials placed in the neighborhood of thereflection point. The substrate beveling may take the form of anarrowing bevel or tapering on one or both sides of the substrate.

[0354] Thus, if an HOHPS of order n is desired, e.g., order n=4, theorder n−1 wave, e.g., order n=3, will be the wave with the closest groupvelocity and hence a potential source of interference. On a substratewith a beveled edge, an absorptive material, such as a sealant, RTVsilicone, epoxy, adhesive or self-adhesive tape, placed beyond the ordern=4 reflection point (where the substrate is thinner) will filter thelower order waves. This material may be placed on one or both sides ofthe substrate. In order to filter the order n+1 wave, a furtheradsorbent material may be placed at the order n+1 reflection point(where the substrate is thicker), which will absorb the order n+1 wavemore than the order n wave due to the concentration of n+1 wave energyat that point. For the special case than n=0, note that the n=1 HOHPSmode to be suppressed relative the ZOHPS mode. One attractive feature ofsuch use of a beveled edge as a reflective mode filter is that glass andother substrates are commonly manufactured with beveled edges.

[0355] Positive Response Sensor

[0356] The scope of the present invention includes embodiments where oneor more sensor subsystems are of the positive-signal type. Here“positive-signal” refers to the use of desired acoustic paths for whicha touch induces a mode conversion required to complete the acousticpath, or produces a wave shifted in phase from the originating wave.Hence the signal perturbation is the generation of a signal amplitude ata delay time for which the previous signal amplitude was small or zero.Corresponding changes, if necessary, are made in the lower levelalgorithm. Embodiments using phase sensitive controllers may not requireany modifications; there is still a vector displacement in I-Q space.Once a delay time and perturbation magnitude are reconstructed, thehigher levels of the touch reconstruction algorithm proceed as theywould without the positive signal feature.

[0357] Before considering an illustrative example of a sensor usingpositive-signal sensor subsystems, recall the following acoustics.Consider the lowest order symmetric and anti-symmetric Lamb waveslabeled as L_(I) and F₁ in, e.g., FIG. 10.18 of the second edition of“Acoustic Fields and Waves in Solids: Volume II” by B. A. Auld. In thelimit that the substrate is very thick, the phase velocities of thesetwo Lamb modes becomes the Rayleigh-wave velocity, and an in-phasesuperposition of L₁ and F₁, “L₁+F₁”, becomes a Rayleigh wave on the topsurface and an out-or-phase superposition of L₁ and F₁, “L₁−F₁”. If thesubstrate is thick, but finite in thickness, then these superposed modesare “quasi-Rayleigh waves”, which indeed are the “Rayleigh waves” usedin actual touchscreens. For substrates of finite thickness, an acousticwave initially launched as “L₁+F₁” quasi-Rayleigh wave on the topsurface will convert into “L₁−F₁” quasi-Rayleigh wave on the bottomsurface after propagating a distance given by

d=(1/2f) v _(R) ² /Δv

[0358] where f is the operating frequency, v_(R) is the Rayleigh-wavevelocity, and Δv is the difference in phase velocity between the L₁ andF₁ modes at the operating frequency. By varying the thickness of thesubstrate, and can control the value of Δv and hence control the valueof d. For commercial Rayleigh-wave sensors as are produced by EloTouchSystems, it is desired that d be very large compared to thedimensions of the touchscreen so that “Rayleigh waves” stay on the topsurface of the touch substrate. Use of 2 or 3 millimeter soda-lime glassat 5.53 MHz satisfies this condition. Alternately U.S. Pat. Nos.5,072,427 and 5,162,618 teach acoustic sensors in which first order Lambwaves sense touches; here the substrate is approximately two wavelengthsthick or thinner, e.g. about 1 millimeter or less of soda-lime glass at5 MHz. Here d is very short so that quasi-Rayleigh wave behavior issuppressed. Having reviewed this background material, let us knowconsider the case of an intermediate substrate thickness (perhapsdetermined empirically) for which d is equal to the distance of anacoustic path across the touch sensitive zone.

[0359] For simplicity, let us first consider the case in which there areno reflective arrays, but rather a straight line of sight betweentransmit and receive transducers as in U.S. Pat. No. 3,673,327 ofJohnson and Fryberger, as shown in FIG., 1(a). As described above, thesubstrate thickness is chosen such that a top-surface quasi-Rayleighwave launched on one side of the touch region will be received as abottom-surface quasi-Rayleigh wave on the other side of the touchregion. By placing, e.g. wedge, transmit and receive transducers on thetop and bottom surfaces of the substrate, both top and bottomquasi-Rayleigh waves can be launched and received. This arrangementsupports four sensor subsystems with top-to-top, top-to-bottom,bottom-to-top, and bottom-to-bottom, acoustic transmission from atransmit transducer to a receive transducer. Before a touch (orcontaminants), the top-to-bottom and bottom-to-top subsystems have largesignals and the top-to-top and bottom-to-bottom subsystems have small(nominally no) signals. A touch will attenuate the top-to-bottom andbottom-to-top signals and create a positive signal response in thetop-to-top and bottom-to-bottom signals.

[0360] For this example, a strongly absorbing touch on the top surfaceof the touch region will “reset” the wave mode as a bottomquasi-Rayleigh wave. Hence a touch not only attenuates the acousticenergy, but also changes the phase between the L₁ and F₁ components.Hence the L₁ and F₁ components will no longer have a phase difference of0° or 180° at the receive transducers, and hence the received wave willno longer be a pure quasi-Rayleigh wave on one surface. The receivetransducers on both surfaces will both detect a quasi-Rayleigh wavecomponent. By this mechanism, the absorbing touch leads to a positivesignal.

[0361] Note that a quasi-Rayleigh wave launched on the top surface andnominally received on the bottom surface will be more heavily absorbed(as measured by the sum of the intensities of the two receive signals)by a touch nearer the transmit transducers than the receive transducers.The converse is true for a quasi-Rayleigh wave launched on the bottomsurface. Hence the ratio of the summed received intensities for burstsfrom the two transmit transducers provides a measurement of positionalong the direction of the acoustic path. With the four signals,top-to-top, top-to-bottom, bottom-to-top, and bottom-to-bottom, a touchcoordinate and touch pressure can be determined with two additionaldegrees of freedom for redundancy or measurement of additional touchcharacteristics.

[0362] The above transducer-line-of-sight scheme generalizes to sensorswith reflective arrays. For example, a rectangular sensor with only “X”arrays could measure X and Y coordinates if it is provided withtransducers and reflective arrays on both the top and bottom of thesubstrate. Note that in this scheme there is no ambiguity for multipletouches regarding which X coordinate to associate with which Ycoordinate. It may be advantageous to thicken the substrate in theregion of the arrays so that quasi-Rayleigh waves between the transducerand the scattering on the arrays stay on the desired surfaces. For sucha rectangular sensor with both “X” and “Y” arrays and transducers on thetop and bottom surface, both X and Y coordinates would be redundantlymeasured.

[0363] Positive-signal sensor subsystems may be considered in which atouch induces other types of mode conversions, e.g. where a wedgetransducer transmits a Rayleigh wave, the transmitting array scattersthe acoustic beam into the touch region in the form of an n=3 HOHPSwave, the receiving array selectively scatters n=4 HOHPS waves intoRayleigh waves which are then received by a Rayleigh-wave wedgetransducer. Mode conversion from n=3 to n=4 HOHPS mode in the touchregion is required to complete the acoustic path. Such a sensor would besensitive to such mode converting perturbations.

[0364] In an embodiment such a positive-signal sensor subsystem iscombined with other sensor subsystems, and dual or multiple modealgorithms provide added characterizations of true and false touches.

[0365] Non-Touchscreen Applications

[0366] The present invention adds much flexibility regarding in sensorgeometry. Maximum sensor size is increased. Sensors need not berectangular. Dramatically non-planar shapes are possible. This opens thedoor for many non-touchscreen applications for which rectangularsubstrates are not appropriate.

[0367] The hexagonal sensor of FIG. 15(b), the triangular sensor of FIG.15(c), the cylindrical sensor of FIG. 19(a), the spherical sensors ofFIG. 21, the basin sensor of FIGS. 22(a) and (b), and thehalf-hemisphere of FIG. 22(c) provide examples of the freedom of sensorgeometry provided by the principles of FIG. 10, FIG. 17, and FIG. 20.This enhances the applicability of acoustic touch sensor technology to,for example, endow robot components with a sense of touch.

[0368] An example of a non-touchscreen application of acoustic touchposition sensing is to detect the presence of acoustically absorptivematter on a surface. For example, as shown in FIGS. 22(a) and (b),acoustic waves are used to determine whether a basin or toilet has beenused, the nature of its contents, and during a flushing or drainingprocess whether and when it is reasonably clean. Thus, a feedbackmechanism is provided for the inside of a wash basin or toilet, whichmay form part of a control system. If it is desirable that the sensormay be able to distinguish solids from liquids, it is preferred thathorizontal shear wave such as a Love wave be employed. Such a wave isviscosity sensitive, and thus is relatively insensitive to water andmore sensitive to viscous materials. Algorithms may thus be implementedto support public policy, e.g., a recent California drought slogan: “Ifit's pee, let it be, if it's brown, flush it down.” In this case, theposition of a mass need not be determined with precision or withoutambiguity.

[0369] The present invention allows the use of redundant information todetermine the position or quality of a touch, allowing differentialsensing and immunity from shadowing in various embodiments. While oftenit is desired to sense coordinate position, in some applications, anaxial position measurement is sufficient. Therefore, the presentinvention also includes one dimensional sensors. For example, practicalapplications of 1-D sensors include components of an apartment buildingdoor-bell system; elevator buttons; musical devices; single degree offreedom manual input devices; and a touch sensor for a security entrysystem. For example, See FIG. 27, which shows a dual mode primarilysingle axis sensing system. In this system, waves of differing modes, aRayleigh wave and an n=4 HOHPS wave are employed. Both waves are emittedfrom a single transducer 2701. The wave is emitted at about 5 MHz, isscattered at a non-orthogonal angle by a reflective array 2702, and isscattered to a second transducer 2703 by another reflective array 2704.The HOHPS wave, on the other hand, is emitted and travels along anorthogonal path 2705. The HOHPS wave passes through the reflective array2704, reflects of a selective n=4 HOHPS reflective boundary 2706, formedas a partially masked beveled edge, and is redirected along its path ofincidence, to the reflective array 2702, back to the transducer 2701. Inthis case, the substrate 2707 is aluminum. FIG. 27(b) shows a timingdiagram for the system according to FIG. 27(a), in which the Rayleigh,FIG. 27(b)(1) and HOHPS, FIG. 27(b)(2), waves overlap in time. Due tothe non-orthogonal path of the Rayleigh wave, some horizontal positioninformation may be extracted from the received signals.

[0370] For security systems, for example, it may be advantageous to beable to verify that the finger or stylus has the expected acousticproperties (e.g., ratio of shear to Rayleigh absorption). Thus, forexample, to enter an area containing biohazard materials, one may wantto require that the operator is wearing dry rubber gloves selected, inpart, to have a distinctive acoustic signature.

[0371] The use of coversheets extend the potential applications for thisinvention. The touch surface may be exposed, or covered. For example, aplastic sheet with spacer dots, provides a number of interestingadvantages. Such a cover sheet protects touch surfaces from scratchesand digs that may disrupt propagation of acoustic waves; particularly ifthe shell is a soft metal like aluminum. By keeping rain off the touchsurfaces, a cover sheet may enable outdoor applications. When provided acoversheet, an acoustic sensor responds more directly to the pressure ofcontact via the compliance of the sheet (rather than sensing theacoustic properties of the contacting material). See, Knowles and Huang,U.S. Pat. No. 5,451,723, which proposes the use of a cover sheet withacoustic touch panels for certain applications.

[0372] Advantageously, “control buttons” can be painted on the touchsurface, or on a corresponding cover sheet. This allows a single surfaceto serve both as sensor and a user input device, providing anopportunity for a unified interface to reduce costs, such as on a toydevice, or to best exploit available surface area. On a toy robot, forexample, a cylindrical aluminum shell is provided with a cover sheethaving graphics. As the toy robot moves, any contact will be sensed.When the robot is motionless, or under other circumstances where contactwith environmental objects is unlikely, e.g., where a touch is notdetected along an axis of movement or expected touch, the sensing may beanalyzed as a potential input from a user.

[0373] The scope of this invention is not limited to transparenttouchscreens placed in front of display devices.

EXAMPLES Example 1

[0374]FIG. 10 represents a generic sensor subsystem including transmitand receive transducers and arrays. This generic sensor subsystemincludes a family of embodiments which differ in the various parameters.

[0375] Later examples will generalize to families of embodiments inwhich the acoustic path between the transmit and receive arrays arescattered one or more times by reflective boundaries. Later exampleswill also generalize to families of embodiments in which the sensorsurface has non-planar geometry. In this example, we consider thegeneric sensor subsystem of FIG. 10.

[0376] In the embodiment of FIG. 10, a set of acoustic paths isassociated with a sensor subsystem. Each member of the set of acousticpaths can be represented by a value between zero and one of a pathparameter “s”. (In cases where a range other than zero to one ismathematically convenient, this can easily be accommodated with a changeof variables.) The acoustic path for a given path parameter starts atthe transmit transducer centered at position T_(t), proceeds along thetransmit array for a distance and direction sA_(t) where it isredirected across the touch sensitive region for a distance anddirection P(s) where it is intercepted by the receive array. Theacoustic path then continues for a distance and direction given bysA_(r) until it ends at the receive transducer centered at T_(r). Thearray locations and orientations need not have any particular relationto Cartesian axis directions or edges of the glass.

[0377] According the present invention, there is no requirement that theset of acoustic paths through the active region be a set of parallelpaths, although in many cases it is convenient to do so in order tosimplify touch reconstruction algorithms.

[0378] There is an acoustic mode associated with each segment of theacoustic paths. Here we define V_(t) to the group velocity, and v_(t) tobe the phase velocity, of the acoustic mode that is emitted from thetransmit transducer and travels down the transmit array and isscattered, and perhaps mode converted, by the transmit array. Similarlywe define V_(p) and v_(p) for the path segment across the touch regionand V_(r) and v_(r) for the segment along the receive array. Theacoustic mode across the touch region must be a surface acoustic wavesuch as Rayleigh or Love waves and Lamb, ZOHPS, HOHPS waves insufficiently thin substrates. The modes along the arrays can be any modewith sufficient coupling to the transducers and the reflective arrayelements.

[0379] For each value of the path parameter, there is an associateddelay time. This delay time is related to the group velocities of themodes used by the following equation.

t(s)=sA _(t) /V _(t) +P(s)/V _(p) +sA _(r) /V _(r)

[0380] (Recall notation where, for example, A_(t) represents themagnitude of the “bold face” vector A_(t).)

[0381] It is generally desirable, but not a requirement, that a geometrybe chosen so that the delay time is a monotonically increasing functionof the path parameter. If so, then a finger touch in the active regioncausing a reduction in signal amplitude at time t(s) must be locatedwithin the locus of points defined by varying α between zero in one inthe following expression.

αP(s)+sA _(t) +T _(t)

[0382] The reflective arrays may be designed with the aid of thespacing-vector method illustrated in FIG. 11. Wave vectors used in thespacing-vector calculations are determined as follows. The wave vectorsk_(t), k_(p)(s), and k_(r), are parallel to A_(t), P(s), and A_(r)respectively. The magnitudes of the wave vectors k_(t)=2π/λ_(t),k_(p)=2π/λ_(p), and k_(r)=2π/λ_(r), dependent on the mode wavelengthsλ_(t), λ_(p), and λ_(r), which in turn arc determined by the operatingfrequency, f, and the phase (not group) velocities v_(t), v_(p), andv_(r), namely λ_(t)=v_(t)/f, λ_(p)=v_(p)/f, and λ_(r)=v_(r)/f. Given thewave vectors as a function of the path parameter, the reflective arrayspacing vectors may be calculated as follows. For the transmit array,the reflector spacing vector can be calculated by the equation below.

S(s)=2πn(k _(t) −k _(p)(s))/|k _(t)−k_(p)(s)|²

[0383] Similarly, for the receive array, the orientation and spacing ofthe reflectors are determined as follows.

S(s)=2πn(k _(p)(s)−k _(r))/|k _(p)(s)−k _(r)|²

[0384] For clarity of presentation, FIG. 10 does not fully does notinclude the following generalizations which are within the scope of thisinvention.

[0385] The vector representing the receive-array scatter location,sA_(r), is more generally expressed as r(s)A_(r) where r(s) is amonotonically increasing function of the path parameter with a rangefrom zero to one.

[0386] FIG. 11 of U.S. Pat. No. 4,642,423 of Adler teaches an arraydesign technique to cause an acoustic beam traveling along an array todeviate from a straight-line trajectory, or more generally to deviatefrom a geodesic trajectory such as a great circle. With the use of thisor other wave guiding techniques, the family of embodiments associatedwith FIG. 10 is extended to cases in which the arrays are not straightline segments.

[0387] A gap without reflectors can be introduced between thetransducers and their corresponding arrays. Such a gap, for example, maybe used to prevent the transducer in question from blocking acousticpaths of another sensor subsystem. More generally, within the formalismof FIG. 10, there is no requirement that the full length of the array ispopulated with reflective elements.

Example 2

[0388]FIG. 12 illustrates examples of specific touch region geometrieswithin the scope of FIG. 10.

[0389] The rectangular touch region shown in FIG. 12(a) is typical ofthe X-coordinate sensor subsystems of current flat rectangular acoustictouchscreen products.

[0390] If all segments of the acoustic path in FIG. 12(a) use the sameacoustic mode, then the spacing-vector formula leads to the prior art45° reflectors with wavelength spacing along the array axes. Forexample, if the incident wave is in the −X direction and the scatteredwave is in the Y direction, then the spacing vector is calculated to beS=(nλ/2,nλ/2) and hence the reflectors are at 45° the spacing betweenreflectors in a direction perpendicular to the reflectors is nλ/{squareroot}2 and the reflector spacing in along the array axis nλ.

[0391] If, instead, the transmit and receive array modes are zerothorder horizontally polarized shear (ZOHPS) waves and the touch regionmode is a Lamb wave, then the spacing vector is calculated to be S=n(λ_(Lamb), λ_(ZOHPS)) {λ_(Lamb) λ_(ZOHPS)/(λ_(Lamb) ²+λ_(ZOHPS) ²)}.This in turn implies a reflector angle θ with respect to array axissatisfying the condition tan(θ)=λ_(Lamb)/λ_(ZOHPS)=v_(Lamb)/v_(ZOHPS).This reflector orientation is that given in equation 2 of U.S. Pat. No.5,072,427. In terms of θ, the magnitude of the spacing vector can bereduced to S=n sin(θ) λ_(ZOHPS) which in turn implies nλ_(ZOHPS)reflector spacing with respect to the array axis. Hence, the arraydesign essentials of U.S. Pat. No. 5,072,427, incorporated herein byreference, are also derivable from the spacing vector formula.

[0392] Going beyond prior art, the principles of FIG. 10 combined withthe vector-spacing formula also allow one to engineer sensor subsystemsfor a variety of other geometries including parallelograms as in FIG.12(b), trapezoids as in FIG. 12(c), and triangles, as shown in FIGS.12(d), 12(e) and 12(f).

Example 3

[0393]FIG. 13 represents an example sensor design that utilizes foursensor subsystems. This design supports control systems which includeanti-shadowing algorithms and algorithms that resolve multi-touchambiguities. The touch region has a width-to-height aspect ratio of{square root}3:1.

[0394] Two sensor subsystems are rectangular as in FIG. 12(a); see FIG.13(a). By itself, FIG. 13(a) has much in common with prior art sensorswith standard X and Y measurements. FIG. 13(a) shows an X transmittransducer 1301, an X transmit reflective array 1302, with reflectiveelements at 45°, an X receive reflective array 1303, with reflectiveelements at 45°, and an X receive transducer 1304. Likewise, a Ytransmit transducer 1305, a Y transmit reflective array 1306, withreflective elements at 45°, a Y receive reflective array 1307, withreflective elements at 45°, and a Y receive transducer 1308 is providedalong an orthogonal set of axes.

[0395] The other two subsystems provide a measurement of a “U” diagonalcoordinate. FIG. 13(b) illustrates these other two sensor subsystems.They are both of the type illustrated in FIG. 12(f). One set of acousticpaths start at the X transmit transducer 1301 and are received by the Yreceive transducer 1308; the touch region for this sensor subsystem istriangular with sides defined by the X transmit array 1302, the Yreceive array 1307, and a diagonal across the touch region. The otherset of acoustic paths start at the Y transmit transducer 1305 and arereceived by the X receive transducer 1304; the touch region for thissensor subsystem is triangular with sides defined by the Y transmitarray 1306, the X receive array 1303, and a diagonal across the touchregion. In both cases, the acoustic paths through the touch region areat a 30° diagonal with respect to the X axis. Together, the touchregions of these two sensor subsystems cover substantially all of therectangular touch region covered by the X and Y sensor subsystems ofFIG. 13(a).

[0396] Reflector angles and spacings are noted in FIG. 13. These valuescan be derived from the principles of FIGS. 10 and the spacing-vectorformula. Reflector angles have been calculated for the case in which allsegments of all acoustic paths use the same acoustic mode a wavelengthλ. The spacing-vector formula supports generalization to embodimentsinvolving mode conversion.

[0397] The arrays shown in FIGS. 13(a) and 13(b) are superposed. Thetransmit array 1302 in front of the X transmit transducer includes both45° and 75° degree reflectors. The transmit array 1306 in front of the Ytransmit transducer includes both 45° and 60° degree reflectors. Thereceive array 1303 in front of the X receive transducer includes both45° and 15° degree reflectors. The receive array 1307 in front of the Yreceive transducer includes both 45° and 30° degree reflectors Thesereflector orientations are appropriate for designs in which no modeconversion at the reflective arrays, i.e. reflector elements areoriented like mirrors so that the angle of incidence equals the angle ofreflectance.

[0398] In a specific embodiment for which the acoustic wavelength is0.0226″, e.g. soda-lime-glass substrate with an operating frequency of5.53 MHz, the reflector spacings along the array axes are an integertimes 0.0226″ for all 45° reflectors, an integer times 0.0121″ for the75° X_(t) reflectors, 0.1687″ for the 15° X_(r) reflectors, 0.0151″ forthe 60° Y_(t) reflectors, and 0.0452″ for the 30° Y_(r) reflectors.

[0399]FIG. 23 shows the timing of received signals for the all-RayleighX-Y-U 30°-diagonal sensor shown in FIG. 13. Other options for acousticmodes and geometrical dimensions of an X-Y-U diagonal sensor will leadto qualitatively similar timing diagrams. As shown, a single acousticemission from either transmit transducer is received by two receivingtransducers. It is noted that the diagonal axis is read in two halves,from separate transducers, hence, a touch 2301 will perturb only onesuch diagonal path signal. Compare FIGS. 23(d) and 23(c).

[0400] In order to analyze the received signals, an anti-shadowingalgorithm may be applied which first searches for a touch in one axisand then the other, reporting a valid output if both are found. If oneis found and the other is not, the diagonal axis signals are analyzedfor touch information. If one of the diagonal signals indicates a touch,then that signal is transformed to produce the missing data and output.Where a touch is not found on another axis, an error condition exists.Where no touch is seen on any axis, no output is reported. With such ananti-shadowing algorithm, consider the case in which an acoustic wavesensing a touch of one sensor subsystem is strongly shadowed by, forexample, a drop of water absorbing a Rayleigh wave or a frozen drop ofwater absorbing a ZOHPS wave. In order to determine a position of atouch, two coordinates are required, which correspond to an X and Y.Where one of the X and Y is subject to interference, the 30° diagonalpath which intersects the touch position, but generally does not alsointersect the interfering substance, may be analyzed to determine theposition of a touch. A relatively simple transform is applied to produceoutputs corresponding to X and Y.

[0401] Alternately, a redundancy-check/multiple-touch algorithm may beemployed. Because the data includes redundant information, in theabsence of interference, the additional data may be used to check thecomputed positions for consistency or to determine the existence andposition of multiple touches. In an initial step, candidate X and Ytouch coordinates are constructed from the X and Y data streams. Thesecandidates are compared for consistency with the diagonal data. Whereall three correspond, a valid output condition exists. Where they do notcorrespond, a different candidate coordinate is proposed and tested.

Example 4

[0402] The sensor of example 3 and FIG. 13 is an X-Y-U sensor in whichthe U acoustic paths are at a 30° diagonal angle and an aspect ratio of{square root}3:1. In this example, we consider an X-Y-U sensor with anarbitrary aspect ratio.

[0403] Let H and W be the height and width of the touch region of anX-Y-U sensor. The U acoustic paths through the touch region have adiagonal angle satisfying tan (Θ)=H/W. The principles of FIG. 10 and thespacing-vector formalism lead to the reflector angles and spacings forthe U subsystems as given in the table below. For the value Θ=30°, theangles and spacings of FIG. 13 are reproduced. The line widths given inthe table correspond to the line width that maximizes the scatteringamplitude; as previously noted these line widths may be used but are notrequired. Angle Spacing Line width X transmit 90° − Θ/2 λ/(1 + cos(Θ))λ/(4 × cos(Θ/2)) X receive Θ/2 λ/(1 − cos(Θ)) λ/(4 × cos(90° − Θ/2)) Ytransmit 45° + Θ/2 λ/(1 + sin(Θ)) λ/(4 × cos(45° − Θ/2)) Y receive 45° −Θ/2 λ/(1 − sin(Θ)) λ/(4 × cos(45° + Θ/2))

[0404] In prototypes constructed according to the present invention, asystem having touch region dimensions of H=6.40″ and W=9.60″ wasconstructed. These are the same touch region dimensions as, thecommercial touchscreen product E284A-693 sold by Elo TouchSystems, Inc.The prototypes were similar in construction, including placement ofreflective arrays, except that the arrays in the prototype sensor weresuperposed arrays including U reflectors as well as standard X and Yreflectors. These prototypes demonstrated the use of diagonal acousticpaths and superposed arrays. The U diagonal angle of the prototypes is33.7° as required by tan(Θ)=H/W=6.40″/9.60″=tan(33.7°). The spacings andorientations of the reflectors for the U sensor subsystems werecalculated using the formulas in the above table.

[0405] All desired sets of acoustic paths were observed in theprototypes. This demonstrates the operation of superposed arrays. Thisalso provides another demonstration of the spacing-vector formalism as ageneral means to enable calculation of reflector spacings andorientations from first principles. Some signal artifacts frominterfering parasitic acoustic paths were observed with theseprototypes, but none that can not be removed or tolerated with the aidof one or more of the following parasitic suppression techniques:reduction of electronic cross-talk in controller and in cabling betweenX and Y burst lines; fine tuning of array foot print geometry; acousticdamping on back side of substrate (e.g. optical bonding or back sideapplication of an OCLI HEA™ anti-reflective coating on a plastic filmwith contact adhesive); line width modulation; increased density ofreflectors elements; and use of a phase-sensitive controller. In allcases in which parasitic acoustic paths were detected in the prototypes,the acoustic path from the transmit to the receive transducers involvedonly one scattering off of an array; no signal artifacts were observeddue to parasitic paths involving multiple reflections.

Example 5

[0406]FIG. 14 provides for the addition of a second diagonal “V”measurement beyond the X, Y, U sensor of FIG. 13. FIG. 14 thereforeillustrates two additional sensor subsystems. The reflective arrays forthis V subsystem are superposed on X,Y, and U arrays similar to thoseFIG. 13. Acoustic paths for one sensor subsystem start at the X transmittransducer 1301 and end at the Y transmit transducer 1305, which in thiscontext serves as a receiving transducer; this sensor subsystem is ofthe type shown in FIG. 12(e). Acoustic paths for the other sensorsubsystem start at the Y receive transducer 1308, now used as a transmittransducer, and are received by the X receive transducer 1304transducer; this sensor subsystem is of the type shown in FIG. 12(d). Inthis case, the X transmit reflective array 1302 includes an additionalset of reflective elements at 15°, the X receive reflective array 1303includes an additional set of reflective elements at 75°, the Y“transmit” reflective array 1306 includes an additional set ofreflective elements at 30°, and the Y “receive” reflective array 1307includes an additional set of reflective elements at 60°. The reflectorspacings are noted on FIG. 14, and may be calculated according to theprinciples according to FIG. 10 and the spacing-vector formula.

[0407] There are many options regarding the acoustic modes which may beemployed. In one embodiment, the U and V subsystems involve no modeconversions, while the X and Y subsystems do. For example, all acousticpath segments may use Rayleigh waves, except for the touch regionsegments of X and Y which use Love waves. Alternatively, all acousticpath segments may use ZOHPS waves, except for the touch regions of X andY which use a lowest order symmetric or anti-symmetric Lamb wave. Inboth these cases, one of the pairs of coordinates (X,Y) and (U,V) sensestouch with a horizontally polarized shear wave and the other with anacoustic mode with significant vertical motion (coupling to pressurewaves in fluids) at the touch surface. A false touch due to a water dropmay be rejected by an anomalously small ratio of shear-wave tonon-shear-wave touch signal.

[0408] If there is no mode conversion in the U and V subsystems, theprinciples of FIG. 10 and the spacing-vector formula lead to thereflector angles and spacings shown in FIGS. 13(b) and 14. However,where mode conversions are implemented, different reflector angles areused. To implement mode conversion in the X and Y subsystems, the 45°reflector angles illustrated in FIG. 13(a) are not used; the tangent ofthese reflector angles will equal the ratio of the phase velocity of themode in the touch region to the phase velocity of the mode propagatingalong the array.

[0409] As with the X-Y-U sensor, the X-Y-U-V sensor need not be limitedto diagonal paths at +30° and −30° angles. The U and V angles areapproximately equal and opposite with magnitudes equal to the inversetangent of the aspect ratio of the touch region. Preferably, thediagonal waves have an angle of between about 10° to 80° to thereflective array, and more preferably between 25° and 65° to thereflective array. The various wave angles preferably differ from eachother by about at least 5°, and more preferably by at least 15°.

[0410] It should be understood that, as an extension of thesetechniques, it is possible to direct a set of acoustic paths having anincremental variation from each transducer to all transducers, includingthe originating transducer. Thus, the system is not limited to, forexample, four sets of acoustic paths. Likewise, while separating thesets of received waves at differing transducers allows use of simple AMreceivers for the acoustic waves, the invention is not so limited and aplurality of sets of waves may be received by a single transducer, withportions received simultaneously.

Example 6

[0411] Touch sensors according to the present invention need not berectangular. A wide variety of polygonal shapes are possible. Forexample, FIG. 15(b) illustrates a hexagonal sensor including sixidentical trapezoidal sensor subsystems of the type of FIG. 12(c).

[0412] In this figure, even numbered transducers 1502, 1504, 1506, 1508,1510, 1512 are transmit transducers and odd numbered transducers 1501,1503, 1505, 1507, 1509, 1511 are receive transducers, although this isnot the only possibility. The six trapezoidal sensor subsystems provideacoustic paths between pairs of transducers as follows: transmit from1512 with receive at 1509; transmit 1502 with receive at 1511; transmit1504 with receive at 1501; transmit 1506 with receive at 1503; transmit1508 with receive 1505; and transmit 1510 with receive 1507.

[0413] The reflector angles of ±60° shown in FIG. 15(a) correspond tothe case in which there is no mode conversion during scattering at thearrays. This can easily be generalized to other acoustic-mode optionsusing the vector-spacing formula.

[0414] Most of the touch panel surface is covered by three sensorsubsystems. If, as drawn, arrays are shortened to make room fortransducers, then there may be the three strips covered by only twosensor subsystems. In this case, the very center of the panel isinsensitive. Alternately, one can back off the transducers and uselonger arrays; perhaps at the expense of increasing the width of theborder region. In addition, a set of paths may be provided which arerectangular, e.g., FIG. 12(a), which encompass the gap region. Threesuch added rectangular sensor subsystems may utilize the following pairsof transmit/receive transducers: 1506 and 1501; 1508 and 1503; and 1510and 1505. When these three rectangular sensor subsystems are added, theneach array has three superposed sets of reflective arrays.

[0415] In theory, a reflective array system may be provided to directacoustic waves to each other reflective array (with a reflectionallowing transmission to reflective arrays disposed on the same side orat an overly obtuse angle). It is preferred, however, in order tominimize acoustic losses, that no more than three sets of reflectiveelements be provided in any reflective array.

[0416] This hexagonal touch sensitive surface has application, forexample, as a system built into a conference table. The sensor isprovided as, for example, a portion of a table top for a round table. Acentral portion of the table includes a hexagonal substrate, each edgehaving a pair of transducers and a composite reflective array having twoor three sets of reflective elements for directing waves to each sidewhich is not adjacent. Thus, with three superposed arrays, waves aredirected at 60°, 90° and 120°. Therefore, to sense coordinate positionalong two axes, potentially 18 wave paths are provided, or ninenon-trivial paths. A significant redundancy therefore exists, providingenhanced immunity to shadowing and allowing resolution of multiplesimultaneous touches, suppression of interference from fixed objects,distinction of finger from palm, and other advantages. Several peoplesitting around the table could simultaneously interact with the system.Due to the large number of sensing paths, this table therefore allowsconferencing and multitouch capability. The touch panel itself may beopaque or transparent. If it is transparent, a reverse projection screenmay be provided on the back side of the substrate upon which an image isprojected. For example, a projective display device may illuminate areverse projection screen laminated to the underside of a 3 mm thickborosilicate glass substrate, upon which an all-Rayleigh wave hexagonalsensor is fabricated; the relatively low acoustic attenuation ofborosilicate glass at 5.53 MHz can support a sensor size with a touchregion large enough to contain a 60 cm diameter circle.

[0417] As shown in FIG. 15(c), the principles may also be applied to atriangular sensor, which in this case also uses the arrays according toFIG. 15(a). In this case, the wavepaths correspond to FIG. 12(d).Alternatively, with array designs differing from FIG. 15(a), atriangular sensor may use three sensor subsystems of the type of FIG.12(e) with the same arrangement of transmit and receive transducersgiven in FIG. 15(c).

[0418] As is evident from this example, and the general principles ofFIGS. 10 and 11, a wide variety of polygons are possible shapes fortouch sensors.

Example 7

[0419] This example illustrates the use of this invention to extendsensor size. For some applications, e.g. electronic whiteboards, largersensor sizes are of considerable interest.

[0420] For a given acoustic mode, operating frequency, and acousticsubstrate, the sensor size is limited by a maximum acoustic path lengthbeyond which further attenuation of the acoustic waves leads tounacceptably weak signal strengths. For example, for 5.53 MHz Rayleighwaves in soda-lime glass, weak signal amplitudes typically are a problemfor acoustic paths longer than about one meter. Use of borosilicateglass or aluminum as a substrate can almost double this maximum pathlength, for otherwise the same system parameters.

[0421] The characteristics of the receiver systems and electronics, theelectromagnetic noise environment affect the limit of detectability andhence affect the numerical value of the maximum acoustic path length.The efficiency of transducers and reflective arrays also influence themaximum path length. Whatever factors limit the acoustic path length,for a given maximum path this invention provides means to extend themaximum size of the sensor. For example, as shown in FIG. 16, a largerectangular sensor is shown having an X, U, V sensor layout along withrepresentative examples of sensor subsystems.

[0422] For the X sensor subsystem of a prior art rectangulartouchscreen, the maximum path length is approximately 2W+H where W and Hare the width and height of the touch region. In the sensor illustratedin FIG. 16, the width is divided into four segments of length S=W/4.Hence each of the X sensor subsystems has a maximum acoustic path lengthof approximately 2S+H=W/2+H. For the U and V sensor subsystems, themaximum path length is 3S/2+{square root}[H²+(3S/2)²]=3W/8+{squareroot}[H²+(3W/8)²]. For a touch region with a 3-to-4 aspect ratio, knownprior art rectangular touchscreens employ a maximum path length of2W+H=(11/3)H, while FIG. 16 gives maximum path lengths of W/2+H=(5/3)Hand 0.46W+H=1.62H<(5/3)H. For given sensor size, the maximum acousticpath has reduced by more than a factor of two. For a given maximumacoustic path length the sensor size can more than doubled. By avoidinglong acoustic path lengths along arrays, the permissible path lengthscrossing the touch region are increased. This increases the maximumpermissible height of the rectangular sensor.

[0423] According to this embodiment, as shown in FIG. 16, acoustic pathsthat must traverse the entire width of the sensor, e.g. as found in a Ysensor subsystems, have been avoided. As a result, there is noacoustic-path-length limitation on the width of the large rectangularsensor, provided there is no limitation on the number of transducers.Thus, while the height of the sensor in FIG. 16 is extended by remainslimited, the width of the sensor can be arbitrarily increased withfurther segmentation of the arrays.

[0424] Delving into further details of the sensor in FIG. 16, there aresix transmit transducers as indicated at the top of the sensor labeledTL, T1, T2, T3, T4, and TR. Six receive transducers are indicated at thebottom of the sensor and are labeled RL, R1, R2, R3, R4, and RR. Thearrays associated with T1, T2, T3, T4, R1, R2, R3, and R4, are triplysuperposed arrays containing reflectors for X, U, and V sensorsubsystems. The vertical arrays are, doubly superposed arrays supportingU and V sensor subsystems only.

[0425] The reflector angles and spacings can be computed from theprinciples of FIGS. 10 and 11. The acoustic paths across the touchregion are at angles of 90° and 90°±θ with respect to the horizontalwhere θ is defined as arctan[(3/2)S/H]. If there is no mode conversion,the reflective arrays at the top and bottom of the sensor havereflectors at angles of 45° and 45°±θ/2 and reflector spacings of nλ andnλ/(1±sinθ). The side arrays have reflector angles and spacings of ±θ/2and nλ/(1−cosθ). One option for the reflector width can be determined byequalizing the reflector line widths and the gaps between reflectors forthe densest reflector spacing. The spacing-vector formula allowscalculation of reflector design parameters for embodiments employingmode conversion.

[0426] To minimize dead regions, it may be advantageous to “shingle” thetop and bottom transducer-array systems, as shown in FIG. 16(c). Bytilting the arrays so that the transducer end of the arrays is at leastone transducer width closer to the edge of the glass than the far end ofthe arrays, the arrays can be extended to eliminate the dead spacescaused by the transducers as shown in FIG. 16(b).

[0427] The X, U, and V, coordinates determined by the sensor subsystemsare linearly related to the delay times for signal perturbations inducedby touches. Each sensor subsystem has is own appropriate constants forthis linear mapping. U and V are related to Cartesian coordinates by thefollowing relations.

U=X+tanθ×Y

V=X−tanθ×Y

[0428] The X, U, and V coordinates are interrelated by the followingequations.

X=(U+V)/2

U=2X−V

v=2X−U

[0429] Hence the Cartesian coordinates (X,Y) are related to X, U, and Vas follows.

(X,Y)=({U+V}/2, {U−V}/{2×tanθ})=(X, {U−X}/tanθ)=(X, −{V−X}/tanθ)

[0430] Any two of X, U, and V is sufficient to determine a touchposition. Furthermore, due to the redundancy and segmentation of thetouch sensitive surface, multiple touches may be simultaneously detectedand their positions analyzed.

[0431] Now consider specific embodiments with no mode conversion havinga rectangular touch region with a 3-to-4 aspect ratio. The value for θis 26.6°, so that the waves traverse the touch region at angles of64.4°, 90° and 116.6° with respect to the horizontal X direction. The Usubsystem reflectors angles are 31.72° for the top arrays, 58.28° forthe bottom arrays, and 13.3° for the side arrays. The X subsystemreflectors of the top and bottom arrays are at 45°. The V subsystemreflector angles are 58.28° for the top arrays, 31.72° for the bottomarrays, and 13.3° for the side arrays. The U subsystem reflectorsspacing is 1.809×nλ for the top arrays, 0.691×nλ for the bottom arrays,and 9.472×nλ for the side arrays. The X subsystem reflectors of the topand bottom arrays have nλ spacing. The V subsystem reflector spacingsare 0.691×nλ for the top arrays, 1.809×nλ for the bottom arrays, and9.472×nλ for the side arrays.

[0432] Further, another embodiment of the sensor has a layout whereinthe dimensions of the touch region are 3 foot by 4 foot, i.e. 60 inchdiagonal. With the layout of FIG. 16(a), the maximum acoustic pathlength is 60″. This is feasible for 5.53 MHz Rayleigh waves in aborosilicate or aluminum substrate. Hence, the sensor design of FIG.16(a) supports a size typical of many electronic white boards presentlyon the market.

[0433] White boards (not necessarily electronic) often have anenamel-on-metal writing surface. An aspect of the present invention isthe use of a Love-wave substrate composed of a thin layer oflow-acoustic-velocity enamel on a low-acoustic loss metal substrate. Forexample, an approximately 100 μm thick lead (or other heavy metal) basedenamel on an 3 mm aluminum substrate, similar to known architecturalpanels in past use. Such a Love-wave substrate may be advantageous insuppressing effects of liquid contaminants such as a trail of drying inkfrom a felt pen and furthermore may be able to provide greater touchsensitivity than ZOHPS waves in a one millimeter thick substrate due tothe Love wave's higher concentration of acoustic power near the surface.

Example 8

[0434] Flexibility of sensor design is further enhanced by the use ofreflective boundaries in sensor subsystems to produce intermediatescattering of acoustic paths. See FIG. 17 which is a generalization ofFIG. 10 in which the acoustic paths undergo an intermediate reflectionbetween the transmit and receive arrays. Similarly, a plurality ofreflections may occur.

[0435] The reflective boundary 1701 may be formed of an array ofreflective elements similar to the transmit and receive arrays. Forexample see item 60 of FIG. 11 of U.S. Pat. No. 4,700,176. The anglesand spacing of reflectors may be calculated using the spacing-vectorformula, that is the reflective boundary's reflector spacing vector isgiven by the following expression (subscript “pt” for path from transmitarray and “pr” for path to receive array).

S(s)=2πn(k _(pt)(s)−k _(pr)(s))/|k _(pt)(s)−k _(pr)(s)|²

[0436] As with transmit and receive arrays, mode conversion is an optionat a reflective boundary 1701.

[0437] Unlike the transmit and receive arrays, which need to bequasi-transparent to acoustic paths propagating along their lengths,reflective boundaries 1701 can be designed to be strongly reflective, solong as no acoustic path need pass through the reflective boundary 1701.

[0438] As with transmit and receive arrays, reflective boundary 1701arrays from different sensor subsystems can also be can superposed withanother sensor subsystem's reflective boundary 1701 or reflective array.

[0439] The reflective boundary 1701 may include an edge of thesubstrate. In this case additional diffraction-grating reflectiveboundary schemes may be considered, such as a faceted edge. If no modeconversion is desired, and the angle of incidence equals the angle ofreflectance, then a simple machined glass edge may be sufficient,particularly for the lowest order plate waves: ZOHPS and lowest ordersymmetric and anti-symmetric Lamb waves. For example, see items 220 and222 of FIG. 17 of U.S. Pat. No. 5,243,148.

[0440] While the acoustic path in FIG. 17 encounters only one reflectiveboundary 1701, these principles generalize to two or more intermediatereflections.

[0441] The delay time in terms of path parameter and group velocities ofmodes along transmit array (V_(t)), transmit path across touch region(V_(pt)), transmit path across touch region (V_(pr)), and receive array(V_(r)) is

t(s)=sA _(t) /V _(t) +P _(t)(s)/V _(pt) +P _(r)(s)/V _(pr) +sA _(r) /V_(r)

[0442] A perturbation in the signal at this time corresponds to a touchwithin the union of the following two sets of points (where 0<α<1).

αP _(t)(s)+sA _(t) +T _(t)

αP _(r)(s)+P _(t)(s)+sA _(t) +T _(t)

[0443] FIG. 11 of U.S. Pat. No. 4,700,176 illustrates the use ofreflective boundaries to reduce the required number of transducers; asensor subsystem is shown in which the acoustic path leaves atransducer, is scattered by 90° by the reflective array, traverses thetouch region, is reflected back across the touch region by a reflectiveboundary, and retraces its path back to the same transducer from whichit started.

[0444] FIG. 17 of U.S. Pat. No. 5,243,148 illustrates the use ofreflector boundaries to pass the acoustic path through mode selectivefilters. In this example, the “reverse reflection” reflective arraydirects acoustic paths away from the touch region through a mode filterbefore a reflective boundary redirects the acoustic paths back towardthe touch region.

[0445] In the context of the present invention, reflective boundariesfurther increase the options for non-orthogonal acoustic paths, theoptions non-rectangular and non-planar sensor shapes, and the optionsfor sensing touches with more than one acoustic mode.

Example 9

[0446]FIG. 17 embodies many possible sensor subsystem geometries, a fewexamples of which are show in FIG. 18.

[0447] In FIG. 18(a), the receive and transmit transducers and arraysare on one side of a trapezoidal touch sensitive region. The receiverand transmit arrays may be superposed, thus allowing the use of a commontransmit/receive transducer.

[0448]FIG. 18(b) is a variation of the trapezoidal scheme in which thereceive and transmit system are lined up in series. In the context of avertical cylinder with periodic boundary conditions, the transmit andreceive arrays may be superposed and use a common transmit/receivetransducer.

[0449] The rectangular sensor subsystem in FIG. 18(c) involves a 180°reflection off the bottom edge. The transmit and receive arrays may besuperposed, or indeed be identical, thus supporting the use of a commontransmit/receive transducer. As presented in FIG. 18(c), with reuse ofthe reflective array and transducer, such sensor subsystems are knownand employed by Carroll Touch in its ZOHPS products for X and Ycoordinate measurements.

[0450] In FIG. 18(d), the transmit and receive arrays scatter indirections opposite to standard commercial rectangular sensors. Thisscheme is shown in FIG. 17 of U.S. Pat. No. 5,329,070 to Knowles. Thisscheme provides additional opportunities for mode filtering of thescattered acoustic waves and may be used to interpose time delays. Thus,a superposed reflective array may be provided with, e.g., reflectiveelements disposed at ±45° to an incident acoustic beam, with onescattered path traveling opposite to the other. One of the pathsintersects a reflective boundary, which redirects it and/or modeconverts it in a desired manner. Further, this configuration may be usedto suppress certain parasitic paths. Finally note that the reflectiveboundary need not act as a mirror parallel to the reflective array, andtherefore may produce an arbitrary reflection angle.

Example 10

[0451]FIG. 19 illustrates a cylindrical sensor which includes sensorsubsystems of the types given in FIGS. 18(b) and 18(c).

[0452] For the purposes of this invention, the meaning of “planarsurface” is extended to include any 2-dimensional surface of Euclideangeometry, i.e. surfaces that can be “unrolled and laid flat” withoutwrinkles or other distortions. A spherical surface is still non-planar;this is an observation related to the map makers' problem for flat mapsof the globe. However, a cylindrical surface may be considered “planar”according to the present invention. A cylindrical sensor surface alongwith acoustic paths can be mapped to a flat surface with correspondingacoustic paths provided that the curvature is always large compared tothe acoustic wavelength; and in fact known touchscreens forcylindrically curved video monitors do not provide particularcompensation for the cylindrical shape. Hence the cylindrically curvedsensor of FIG. 19 may serve to illustrate application of FIG. 18.

[0453] The sensor in the form of a complete cylinder poses aninteresting topological twist to “planar” sensor geometry. The sensor ofFIG. 19 takes advantage of the periodic boundary conditions of a fullcylindrical surface 1901. As is apparent from inspection of FIG. 19,this eliminates the need for any vertical arrays.

[0454] The touch sensor of FIG. 19 includes the superposition of twosensor subsystems 1902, 1903 of the type of FIG. 18(b) and two sensorsubsystems 1904, 1905 of the type of FIG. 18(c). There are tworeceive/transmit transducers 1906, 1907 each aimed at superposedreflector array 1908, 1909 containing three sets of reflectors.

[0455] With the aid of the principles of FIGS. 10 and 11, there are manyoptions regarding acoustic modes. The choice of acoustic modes willaffect the design of the reflective boundary at the top of the cylinder.If lowest order plate waves are used across the touch region, i.e.ZOHPS, lowest-order symmetric Lamb, or a flexural wave, the reflectiveboundary can simply be a machined edge as illustrated in FIG. 19(a). Forother types of surface acoustic waves, reflective-array type reflectiveboundaries may be used.

[0456] If there is not mode conversion at the reflective arrays, thenthe reflector angles are 45° for the sensor subsystems of the type ofFIG. 18(c), and the reflectors for the trapezoidal subsystems are atangles of 45°±θ/2 where tan(θ)=πR/2H. If mode conversion is desired,then the spacing-vector formula may be used to calculate reflectorangles and spacings.

[0457] Note that a burst from a transducer will generate three signals.For some delay times, all three received signals will be active. Severalapproaches can be used to disentangle such simultaneously receivedsignals.

[0458] Signals from the rectangular subsystems of the type of FIG. 18(c)are isolated. For these signals, the receive transducer is the same asthe transmit transducer, in contrast to the four signals from thetrapezoidal subsystems of the type of FIG. 18(b). This is an example ofusing distinct receive transducers to separate signals generated by acommon transmit pulse.

[0459] In trapezoidal sensor subsystems, for a given choice of transmittransducer (the other choice simply reverses the directions of theacoustic paths), a burst generates two signals in the same time windowreceived by a common receive transducer. One approach here is to designthe reflector spacings of the two sensor subsystems to correspond to twodifferent operating frequencies. The frequency tuning of the receiverelectronics is then used to separate the signals; the transmit burst maybe broad band or a sequence to bursts at different frequencies.

[0460] Another approach is to use a phase-sensitive controller. The twosimultaneously received signals are allowed to combine with anuncontrolled phase at the receiver. However, regardless of the relativephase between the two received signals, a touch attenuation in onesignal will always be recognized by an amplitude change, or phasechange, or both, of the combined signal.

[0461] Signal separation with a phase sensitive controller may result inan ambiguity in the identification of which perturbation in the combinedsignal corresponds to which component signal. See dotted ghost paths1910 shown in FIG. 19(b). For the sensor of FIG. 19, such ambiguitiescan be easily resolved with the aid of the coordinate data from therectangular sensor subsystems.

[0462]FIG. 19 is but one of many possible cylindrical sensorconfigurations. Other examples include systems with a touch surface onan inside surface of a cylinder; a single transducer with reflectivearray around full circumference; top and bottom arrays, side-by-sidearrays with separate transducers rather than superposed arrays; etc.

Example 11

[0463]FIG. 28 shows a planar sensor system which faces the same types ofambiguities as the cylindrical sensor according to FIG. 19. In thisembodiment, a single transducer 2801 and superposed reflective array2802 generates and receives sets of waves 2803, 2804 traveling at anangle to one another. In this system, as shown in FIG. 28(b2), a singletouch produces a pair of perturbations in a received signal. The averagetime delay for the pair of signal perturbations represents the distancealong the array from the transducer, while the separation represents thedistance from the bottom edge of the substrate. Note that a singlesensor subsystem observes the touch twice due to the forward andbackward wave paths. The embodiment of FIG. 28(a) includes a third setof wave paths 2805 which is orthogonal. In this case, one set of thereflective elements in the array 2802 is used to mode convert a Rayleighwave emitted from the transducer to a HOHPS wave at right angles.

[0464] The sensor of FIG. 28(a) provides redundancy that may supportanti-shadowing algorithms, multiple-touch algorithms, as well asdual-mode touch-characteristic algorithms.

[0465] FIGS. 28(b) and 28(c) further show that these three wavepaths maybe used to determine the positions of a pair of touches. The methodfirst looks for perturbations of the rectangular wave sets 2810. Fromthese, the X coordinate is estimated 2811. Perturbations in the “W”shaped wavepaths are next determined 2812. An iterative loop 2813 isthen commenced to review all pairs of perturbations. The average delayis calculated 2814. For each perturbation of the rectangular path 2815,the consistency of the “W” shaped paths is determined 2816. Further,since the rectangular wave is a shear wave and the “W” wave is aRayleigh wave, the attenuation ratio may be determined to eliminatewater droplet shadowing effects 2817. The confirmed touch position isthen calculated 2818, and output 2819. Further rectangular pathperturbations are then analyzed 2820, and then the iterative loop 2813incremented 2821.

Example 12

[0466] The concepts of FIG. 10 generalize to non-planlar, i.e.non-Euclidean, surfaces. On a non-planar surface, acoustic wavesnaturally travel on geodesics of the surface. For example, on aspherical surface, acoustic waves naturally follow great circles. Theline segments of FIG. 10 therefore generalize to the geodesics of FIG.20.

[0467] All three segments of the acoustic path shown in FIG. 20 aregeodesics. The path parameter “s” can be any parameter that is smoothlyand monotonically related to the arc length along the reflective arrays.The delay time as a function of the path parameter, t(s), can bedetermined by the sum of the arc lengths of the segments, each dividedby the group velocity of its acoustic mode.

[0468] A closed analytic expressions for t(s) typically does not existfor a general complex curved surface. Once the geometry of the sensor isknown or proposed, numerical calculations may be needed to calculatet(s) as well as the wave vectors needed by the spacing-vector formula tocompute reflector angles and spacings as a function of s.

[0469] Reflector spacing and orientations are determined as a functionof the array and path parameter s by considering a small quasi-planarneighborhood in which the scattering takes place, and then applying thewave vector analysis in the same way it is applied to planar coordinatesubsystems. In this context, FIG. 11 represents a small quasi-flatregion of a general curved surface. The spacing-vector formula isequally applicable to planar and non-planar sensors.

[0470] As shown in FIG. 17, FIG. 10 can be generalized to cases in whichthe acoustic paths encounter reflective boundaries. While not explicitlyshown, the same is understood for FIG. 20. Reflective boundaries are noless applicable to non-planar surfaces as they are to planar surfaces,and in fact may advantageously be employed to increase options forsensor geometry or to simplify construction of the touch sensor.

[0471] As noted with FIG. 10, wave guiding effects can be used to designtransmit and receive arrays that cause the corresponding acoustic pathsto deviate from line segments. Likewise, FIG. 20 generalizes to cases inwhich the transmit and receive segments deviate from geodesics.

[0472] The principles of FIG. 20 enable numerous possible shapes fornon-planar sensor design. A few examples follow. While there ispedagogic value to emphasize special cases which can be analyzedanalytically, e.g., sections of a sphere, the scope of the presentinvention is not subject to such limitations.

Example 13

[0473] FIGS. 21(a) and (b) provides an example of a non-planar sensor.Here the touch surface is a section of a sphere, qualitativelycorresponding to the Earth's surface between the equator and the arcticcircle.

[0474] This sensor contains four sensor subsystems as follows.

[0475] A burst from transmit transducer T1 will be scattered at a 90°angle and proceed up a “line of longitude” until it is reflected by areflective boundary near the top of the spherical cap, and retraces itspath back to T1. This sensor subsystem covers a “twelve hour time zone”.Similar acoustic paths starting and ending at transducer T2 provide asecond sensor subsystem which covers the other “twelve hour time zone”.Together, these two sensor subsystems provide a φ coordinate measurementwhere T1 senses a touch if φ is negative and T2 senses a touch if φ ispositive.

[0476] Not shown in FIG. 21(a) are the “u” acoustic paths that start attransducer T1 and end at transducer R1. As shown in FIG. 21(b), at anangle u with respect to the T1/T2 transducer pair, the transmittedacoustic beam is scattered onto a great circle. This great circle istilted with respect to the vertical by an angle θ and passes between theR1/R2 transducers and the polar hole. When it intersects the equator, itis scattered onto the equator and completes its journey to R1.

[0477] Shown in FIG. 21(b) is an acoustic path of the “v” system whichis very similar to the “u” sensor subsystem. This time the burst comesfrom T2 and the signal is received at R2. The great-circle geodesic isagain inclined at a tilt of angle θ, but this time goes between theT1/T2 transducers and the polar hole and the associated reflectiveboundary used by the φ sensor subsystems.

[0478] Neither the u or the v sensor subsystems cover the full touchregion. However (neglecting possible dead regions due to the finite sizeof transducers), all points on the touch surface are covered either bythe coordinate pair (u,φ) or by (v,φ). Two dimensional coordinates canbe sensed for the entire touch surface with the aid of an anti-shadowingalgorithm; here the shadows in question are due to the polar hole.

[0479] Looking at more detail at the sensor geometry, if any two of thethree coordinates, φ, u, v are measured, then the coordinates of thetouch on the spherical cap, (Θ,φ) can be determined. Here we define theangle of the touch with respect to the vertical direction, Θ, such thatΘ≡0 on the “north pole” and Θ=90°=π/2 at the “equator”, where the arraysare situated. Possible measured values of Θ are in the range θ<Θ<π/2.

Θ=arctan(tan(θ)/sin(Δφ))=arccot(sin(Δφ)×cot(θ)) where

Δφ=(π−u−v)/2 for φ>0

Δφ=(u+v−π)/2 for φ<0

[0480] or

Δφ=φ−u for φ>0

Δφ=|φ|+u−π for φ<0

[0481] or

Δφ=π−φ−v for φ>0

Δφ=v−|φ| for φ<0

[0482] If φ is not measured directly, it can be determined from u and vas follows.

If (u+v)<π, then φ>0 and φ=(u−v)/2+π/2

If (u+v)>π, then φ<0 and φ=(u−v)/2−π/2

[0483] If φ and one of u and v is known, the other can be predicted asfollows.

u=2φ+v−π for φ>0 or u=2φ+v+π for φ<0

v=π+u−2φ for φ>0 or v=−π+u−2φ for φ<0

[0484] The angles u and v have ranges between 0 and π and are linearlyrelated to delay times.

[0485] With the aid of the spacing-vector formula and the principles ofFIG. 20, there are many options for the choice of acoustic modes. As asimple example, consider the case in which only one acoustic mode isused for all acoustic path segments. In this case, the equatorial arrayswill include three sets of superposed reflector elements as follows: 45°reflectors with nλ spacing; 45°−θ/2 reflectors with nλ/(1−sin(θ))spacing; and 45°+θ/2 reflectors with nλ/(1+sin(θ)) spacing. Also, inthis case, the reflective boundary may be formed of a set of concentricrings with a surface spacing of λ/2.

[0486] There are many substrate options: glass, aluminum,enamel-on-aluminum Love-wave substrate, etc. The choice of acoustic modeand substrate do not affect the sensor geometry except in determiningthe maximum size. For example 5.53 MHz Rayleigh waves on aluminum cansupport sizes with a diagonal dimension larger than 30 centimeters.

[0487] In a particular embodiment, a hemispheric aluminum dome isprovided approximately 300 mm in diameter. Near the “equatorial” concaveopening, a pair of reflective arrays are provided on the outer surface,each extending almost halfway around the hemisphere and nearly meetingat each side. On each end of each reflective array is provided anultrasonic transducer, such as a piezoelectric ceramic element, whichmay be mounted on a wedge, to generate or receive an acoustic wavetraveling parallel to the axis of the reflective array.

[0488] Near the apex of the dome, another reflective member is provided,having a diameter of approximately 100 mm. This apical reflector may bestrongly reflective for perpendicular incident waves and weaklyreflective for possible parasitic acoustic paths at other angles ofincidence.

[0489] Each reflective array includes three sets of reflective elements:

[0490] 1. 45° to axis of symmetry of hemisphere with spacing of nλ

[0491] 2. 45°+θ/2 (35.5°) to the equatorial plane of the arrays withspacing of nλ/(1−sinθ)

[0492] 3. 45°−θ/2 (54.5°) to the equatorial plane of the arrays withspacing of nλ/(1+sinθ)

[0493] Mirror reflection ambiguities in these reflection angles areresolved by considering the desired acoustic paths along with theangle-of-incidence-equals-angle-of-reflectance criteria. θ is the anglebetween the center of the hemisphere of the upper reflective member,about 26°.

[0494] In this case, portions of a wave transmitted from a firsttransducer along one of the pair of arrays are emitted along greatcircles of the hemisphere, which are then received by the otherreflective array, following a path parallel to the reflective array to areceiving transducer. Other portions of the wave are directed directlytoward the apical reflective member and back down toward the originatingreflective array and originating transducer. Therefore, at any time, awave emitted by one transducer is received by that same transducer aswell as one receiving transducer associated with the other array.Therefore, both systems may be operative simultaneously to receiveacoustic waves without substantial mutual interference. The transmittransducers T1 and T2 may emit acoustic bursts sequentially.

[0495] Alternately, these arrays may be shingled, inclined at a smallangle to allow the transducer of one array to sit distal to an end ofthe other array. Of course, the angles and spacing of the array must becompensated for this inclination per the spacing-vector formula. In apreferred embodiment, the transducers are tucked just below the equatorand the corresponding reflector arrays follow great circles that endpass just above the transducers at the opposite side.

[0496] Furthermore, there may be greater than two transducers andarrays, allowing a plurality of sensing waves to be emitted by atransducer and received by a plurality of transducers, according to theprinciples set forth herein.

[0497] It is noted that, on any substrate, and in particular insubstrates which are nonplanar, the coordinate system employed to definethe perturbation position need not be in a Cartesian or pseudo-Cartesiansystem, and therefore may be expressed in a polar coordinates, or inother terms. Further, in certain instances, extrinsic factors, such asan overlay or superimposed image may be used to define valid entries,and therefore the ambiguities in the input position are need notnecessarily be fully resolved solely through acoustic wave perturbationanalysis in every instance in order to provide a useful output.

Example 14

[0498] FIGS. 21(c) and 21(d) provide another example of a non-planarsensor utilizing the principles of FIG. 20. Again we consider a sectionof a sphere. This time the touch surface corresponds to everything northof the “Tropic of Cancer”, and the region between the equator and theTropic of Cancer is available for arrays and transducers. This system isdescribed in further detail below.

[0499] The dome sensor shown in FIGS. 21(c) and 21(d) is hemisphericalin shape. The touch region is above the “Tropic of Cancer” at 23.5° Nlatitude and is redundantly covered with no dead regions by three pairsof sensor subsystems. Arrays and transducers are placed in the region ofthe hemisphere between its base or equator and the Tropic of Cancer. Thearrangement of transducers and arrays are shown in the flat-mapprojection given in FIG. 21(c). One of the six sensor subsystems isillustrated from a top view perspective in FIG. 21(d).

[0500] In the simplest embodiment with six sensor subsystems, each arrayarc in FIG. 21(c) corresponds to a single set of reflective elementsforming an array. However, according to the present invention, it isnoted that these arrays may be superposed to support additional sensorsubsystems, and therefore each transducer may be associated with aplurality of wave paths, providing further redundancy. The simplestembodiment is described in more detail below.

[0501] Equally spaced around the equator are six pairs of transducers,one transmit and one receive. Each transducer pair supports one sensorsubsystem. Each of the following three sensor-subsystem pairs fullycover the touch region above the Tropic of Cancer: R1/T1 and R4/T4;R2/T2 and R5/T5; and R3/T3 and R6/T6.

[0502] For clarity of presentation only, FIG. 21(c) shows a gap betweenthe end of the transmit array for T1 and the receive array for R4, andlikewise for other diametrically opposed transmit and receivetransducers. In practice, it is desirable to extend both arrays so thatthere is an overlap. This assures that there is no dead region, and infact an overlap between, for example, the R1/T1 sensor subsystem and theR4/T4 sensor subsystem. The overlapping portions of the arrays havereflector elements approximately mirror reflected with respect to thearray axis.

[0503] Consider now in more detail an individual sensor subsystem, i.e.,the R1/T1 sensor subsystem shown in FIG. 21(d), the transmit arrayfollows a section of a great circle that intersects the X axis and isrotated by an angle Θ about the X axis with respect to the equatorialplane. The tilt angle, say Θ=20°, is less than the 23.5° latitude of theTropic of Cancer.

[0504] In analyzing this array, let R be the radius of the hemisphere.Then the transmit array follows the following trajectory on the surfaceof the hemisphere.

x(s)=R·cos(πs/2)

y(s)=R·sin(Θ)·sin(πs/2)

z(s)=R·cos(Θ)·sin(πs/2)

[0505] The definitions used here for the x, y, and z directions areshown in FIG. 21(d). Similarly, the trajectory for the receive array isas follows.

x(s)=R·cos(πs/2)

y(s)=R·sin(Θ)·sin(πs /2)

z(s)=−R·cos(Θ)·sin(πs /2)

[0506] In these formulae, s is the path parameter which nominally variesfrom zero to one as the distances from the transducers increases. Inthis example, the array will start for a small positive value of s inorder to make room for the finite sized transducer, and the array willend at a value of s slightly greater than one in order to provide theoverlap between the sensor subsystem pairs discussed above.

[0507] Now consider the (θ,φ) coordinate system for the surface of thehemisphere defined by the following relations.

−π/2<θ<π/2

0<φ<π

x(θ,φ)=R·cos(θ)·cos(φ)

y(θ,φ)=R·cos(θ)·sin(φ)

z(θ,φ)=R·sin(θ)

[0508] In terms of this coordinate system, the transmit array followsthe trajectory:

θ(s)=arcsin(cos(Θ)·sin(πs/2))

φ(s)=arctan(sin(Θ)·tan(πs/2))

[0509] and the receive array follows the following trajectory:

θ(s)=−arcsin(cos(Θ)·sin(πs/2))

φ(s)=arctan(sin(Θ)·tan(πs/2))

[0510] The geodesic connecting the transmit and the receive arrays forthe path parameter s is a segment of a line of longitude with respect tothe z axis, namely the following section of a great circle.

−arcsin(cos(Θ)·sin(πs/2))<θ<arcsin(cos(Θ)·sin(πs/2))

φ=arctan(sin(Θ)·tan(πs/2))

[0511] There are many options regarding choice of acoustic modes, andthe particular spherical configuration does not alter the generalprinciples of the invention. Let us consider in more detail the case inwhich the same acoustic mode propagates along both the transmit andreceive arrays with group velocity V, while the mode, perhaps different,traversing the touch region has the group velocity V′. The delay time asa function of path parameter is given as follows.

T(s)=(R·(πs/2))/V+2R·arcsin(cos(Θ))·sin(πs/2))/V′+(R·(πs/2))/V

[0512] The delay time can also be expressed in terms of the coordinate φof a touch which intercepts the acoustic path.

T(φ)=(2R/V)·arctan(tan(φ)/sin(Θ))+2R·arcsin(cos(Θ)·sin(arctan(tan(φ)/sin(Θ)))/V′

[0513] With this analytic expression, a look-up table may be calculated.Such a look-up table can be used in real-time microprocessor code toconvert measured delay times of signal perturbations into the touchcoordinate φ.

[0514] More generally, while explicit mathematical analysis may be ableto determine a touch location on the surface, this analysis is notnecessary in some cases. Rather, the transducers produce a set ofoutputs for a given touch condition, e.g., a location. By empiricallydetermining a signature of this touch condition, the controller will beable to determine when this input condition subsequently occurs.Further, with a number of such conditions determined, an interpolationor statistical determination of the condition of an input determined,even if it does not identically correspond to a previously determinedinput condition. A lookup table is one way to store the data.Alternately, the data may be stored as coefficients of a compensationalgorithm for mapping the input space into a desired output space.

[0515] The transducer pairs R1/T1 and R4/T4 provide complete coverage ofthe touch coordinate φ over the entire touch region.

[0516] Similarly R2/T2 and R5/T5 provide measurement of a touchcoordinate u which is an equivalent to φ except that the polar axis,while still in the x-z plane, is rotated 60° with respect to the z axis.Likewise R6/T6 and R3/T3 provide a touch coordinate v which is anequivalent to φ rotated −60°. The three coordinates φ, u, and v provideredundant coverage of the dome sensor. In terms of x, y, and zcoordinates, φ, u, and v are defined by the following relations.

φ=arctan(y/x)

u=arctan{y/[(1/2)x+({square root}3/2)z]}

v=arctan{y/[(1/2)x−({square root}3/2)z]}

[0517] The touch coordinate θ can be determined from φ, u as follows.

θ(φ, u)=arctan [2cot(u)·sin(φ)/{square root}3−cos(φ)/{square root}3]

[0518] Likewise, the touch coordinate θ can be determined from φ, v asfollows.

θ(φ, v)=−arctan [2cot(v)·sin(φ)/{square root}3−cos(φ)/{square root}3]

[0519] If θ(φ, u) and θ(φ, v) agree, then (φ, u, v) form a selfconsistent triple of delay times; the meaning of self consistency of atriple is discussed above, e.g., in connection with item 2403 of FIG.24(a). Thus, this sensor supports anti-shadowing andmultiple-touch/redundancy-check algorithms.

[0520] If we define δθ=θ, δφ=φ−π/2, δu=u−π/2, and δv=v−π2, then the topof the dome sensor corresponds to the values δθ=0, δφ=0, δu=0, and δv=0.Taylor expanding the above relations about the top of the sensor givesthe following approximate relations.

δθ=δφ/{square root}3−2δu/{square root}3

δθ=−δφ/{square root}3+2δv/{square root}3

δθ=(−δu+δv)/{square root}3

δφ=δu+δv

[0521] Note the similarities for the planar hexagonal sensor of FIG.15(b) where Y is the coordinate measured by the two sensor subsystemsusing transducers 1502, 1511, 1508 and 1505, U is the coordinatemeasured by the two sensor subsystems using transducers 1504, 1501, 1510and 1507, V is the coordinate measured by the two sensor subsystemsusing transducers 1512, 1509, 1506 and 1503, and the center of thesensor corresponds to X=Y=U=V=0. $\begin{matrix}{U = {{{- \left. \sqrt{}3 \right.}X\text{/}2} + {Y\text{/}2}}} & {or} & {X = {{{+ Y}\text{/}\left. \sqrt{}3 \right.} - {2U\text{/}\left. \sqrt{}3 \right.}}} \\{{V = {{\left. \sqrt{}3 \right.X\text{/}2} + {Y\text{/}2}}}\quad} & {or} & {X = {{{- Y}\text{/}\left. \sqrt{}3 \right.} + {2V\text{/}\left. \sqrt{}3 \right.}}} \\\quad & \quad & {{X = {\left( {{- U} + V} \right)\text{/}\left. \sqrt{}3 \right.}}\quad} \\\quad & \quad & {{Y = {U + V}}\quad}\end{matrix}$

[0522] There is a quantitative analogy between X, Y, U, and V with δθ,δφ, δu, and δv in the small quasi-flat region at the top of the sensorof FIG. 21(d). In this sense, The sensor of FIG. 21(d) is a non-planargeneralization of the sensor of FIG. 15(b). Similarly, there arenon-planar generalizations of other planar sensors geometries.

[0523] Reflector spacing and angles can be calculated using previouslydiscussed principles. Let us refer again to this first sensor subsystemin FIG. 21(d). For the transmit array, the reflector spacing vector isS=2πn(k_(t)(s)−k_(p)(s))/|k_(t)(s)−k_(p)(s)|² where k_(t)(s) andk_(p)(s) can be calculated from the known array trajectory (θ(s), φ(s))given above by the following expressions.

k _(t)(s)=(2π/λ)·(−sin(πs/2), sin(Θ)·cos(πs/2), cos(Θ)·cos(πs/2))

k _(p)(s)=(2π/λ′)·(−cos(φ(s))sin(θ(s)), −sin(φ(s))sin(θ(s)), cos(θ(s))

[0524] Here λ represents the wavelength of the acoustic mode travelingalong the transmit array and λ′ represents the wavelength traversing thetouch region.

[0525] Note that the maximum acoustic path length for the sensorsubsystems is (2π−2Θ)R. For Θ=20°, this becomes 5.585*R. For Rayleighwaves at 5.53 MHz on aluminum or borosilicate glass substrates, thismeans the dome sensor can have a radius in excess of 10 inches. Evenlarger sizes are possible if a lower operating frequency is used, orother means are provided to reduce acoustic attenuation or tolerateweaker signal amplitudes.

[0526] Therefore, an application for the hemispheric dome sensoraccording to this embodiment is, for example, in an interactive museumenvironment. For example, a 20 inch (or a ½ meter) diameterborosilicate-glass dome sensor with a reverse-projection screenlaminated on the back side may be provided. Star patterns of the nightsky, or a section of the Earth's globe may be projected onto the sensor.This system could support a table-top hands-on planetarium or aninteractive globe exhibit. The touch surface, arrays, and transducersmay be placed on the concave side of the sensor; for example, aninteractive touch sensitive aquarium portal may be provided, perhaps incombination with an ultrasonic fish finding/identification system, inwhich the user points to sea creatures that may swim by. Many otherapplications can be imagined.

Example 15

[0527] FIGS. 22(a) and 22(b) provide an example which illustrates theinherent geometric flexibility of the present invention. It shows abasin which may be thought of as a flattened and otherwise distortedhemisphere with a hole in it for a drain. Such a sensor geometry may beof interest as a basin perhaps containing a liquid. Furthermore thetouch sensitive surface is on the inside rather than the outside. Thereflective arrays 2201, 2202, 2203, 2204, 2205, 2206 are disposed withtopological similarity to the hexagonal sensor of FIG. 15(b); there aresix superposed arrays, each with one transmit 2207, 2208, 2209, 2210,2211, 2212 and one receive transducer 2213, 2214, 2215, 2216, 2217,2218. As with the hexagonal sensor of FIG. 15(b), a third set ofreflectors may be superposed on each array to support sensor subsystemsinvolving opposite pairs of arrays.

[0528] The sides of the basin 2200 are vertical at the locations of thetransducers and arrays. Thus the intersection of a horizontal plane atthe level of the transducers and arrays with the basin forms a geodesicloop. The acoustic paths along the arrays follow sections of this closedloop geodesic.

[0529] For the transmit and receive arrays of each sensor subsystem, wedefine the path parameter “s” to be arc length of the path along thearray from the transducer an ay divided by the total arc length of thearray.

[0530] Conceptually, the geodesic paths across the touch region forvalue s can be determined as follows. A string is anchored on thetransmit array corresponding to the value of the path length parameters. The string is looped over the convex surface of the basin 2200 sothat it intersects the receive array at the location corresponding tothe path length parameter s. The string is pulled taught, and the lengthof the string between the arrays and the directions of the string atboth arrays is observed; this determines the path length of the geodesicacross the touch sensitive zone as well as the directions of the wavevectors of the geodesic where scattering takes place on the transmit andreceive arrays. In practice, this conceptual scheme serves as themathematical basis of a computer simulation algorithm that solves theacoustic path geometry. In this manner, all relevant geometricinformation of FIG. 20 may be determined.

[0531] If the basin 2200 is very deep, e.g. not a flattened hemispherebut rather a stretched hemisphere, then the geodesics between the arraysmight not pass through the desired touch region. In the string analogy,pulling the string tight may cause the string to slip off the desiredtouch zone. In this case, the design engineer can either flatten thebasin geometry or introduce intermediate scatterings in the acousticpath with reflective boundaries.

[0532] For any choice of acoustic modes and substrate options, theprinciples of FIG. 20 and the spacing-vector formula allow calculationof reflector angles and spacings. As is typical of present commercialacoustic touchscreen design methods, modulation of array reflectivity(e.g., via reflector density, reflector height, or line width) can bedetermined iteratively by building prototypes, observing signaluniformity (or lack thereof), and improving the modulation of arrayreflectivity. Means are thus available to design reflector arrays forthe sensor in FIGS. 22(a) and 22(b).

[0533] As an illustrative example, consider the following choice ofacoustic modes and substrate. The basin 2200 is formed of aluminum witha thickness of 1 mm which smoothly increases to a thickness of 3 mmwithin a centimeter of the arrays and transducers. The inside of thealuminum basin is enamel coated, with an appropriate type and thicknessof enamel to support Love waves at about 5 MHz, e.g. 100 microns of lead(or other heavy metal) based enamel. For the acoustic paths across thetouch region, the lowest order Love wave is used. Along the reflectivearrays, e.g., a third order symmetric Lamb-type wave as modified by thepresence of the enamel coating propagates. The array reflectors areformed as modulations in an otherwise smooth inside surface of thealuminum basin and may be fabricated by milling, scribing, chemicaletching, photoetching, photoresist, or stamping before application ofthe enamel coating. The transducers (coupling to the Lamb-type waves)are wedge transducers and are bonding to the outside or convex surfaceof the aluminum basin. Thus, both the transducers and reflective arraysare protected from the environment in the basin 2200.

[0534] Note that for this particular choice of modes and substrate, thebasin 2200 can be partially or completely filled with water and stillrespond to and distinguish a touch due to a finger of similarperturbation that provides viscous damping at the touch surface.

[0535] From the perspective of perturbation analysis algorithm design,the drain pipe hole 2219 shown in FIG. 22(b) maybe regarded as ageneralized “contaminant”. In this regard, note that the sensor designof FIGS. 22(a) and 22(b) has sufficient redundancy to supportanti-shadowing algorithms.

[0536] After a use of the wash basin or toilet is detected, a water flowor flush is manually or automatically initiated. In this case, theacoustic sensor may be used to determine when the bowl is emptied, andcease water flow when the contents are evacuated. In the case of atoilet, which operates according to a fixed cycle, a minimal cycle maybe preprogrammed, detecting when such a cycle is necessary, withrepetition as required to fully evacuate the bowl. Otherwise, a rate orduration of water flow may be modulated. Thus, a closed loop washing orflushing cycle control is possible.

[0537] Applications of acoustic sensors such as the above applicationsdemand sensor designs of complex non-planar geometry as is enabled bythe present invention.

Example 16

[0538] In some cases it may be advantageous to use the same spacingvector of the same reflective array for more than one sensor subsystem.This further extends the design options within the scope of thisinvention.

[0539] As an illustrative example, consider a reflective array along theX direction with a single set of uniformly spaced 45° reflectors on asoda-lime glass substrate. The array is illuminated by a transmittransducer which generates Rayleigh waves at either 5 MHz with or 2.5MHz. The Rayleigh wavelength is 0.025″ at 5 MHz and 0.050″ at 2.5 MHz.The spacing of the reflectors along the axis of the array is 0.100″,that is, four Rayleigh wavelengths at 5 MHz and two Rayleigh wavelengthsat 2.5 MHz.

[0540] The spacing vector for this reflective array is S=(−0.050″,0.050″). This spacing vector supports 90° scattering of Rayleigh wavesat 5 MHz, 90° scattering of Rayleigh waves at 2.5 MHz, and, as discussedbelow, for certain discrete thickness of the glass substrate, scatteringof 5 MHz Rayleigh waves at 71.56° into a plate wave.

[0541] The incident wave vector for Rayleigh waves is k_(I)=(2π/λ, 0) isevaluated as (251.3 inch⁻¹, 0) at 5 MHz and (125.7 inch⁻¹, 0) at 2.5MHz. The corresponding 90° reflected wave vectors k_(R) are given by (0,251.3 inch⁻¹) and (0, 125.7 inch⁻¹). In the spacing vector where V isthe acoustic group velocity (assuming all modes the same) and t is theY-to-X delay time. Similarly, if the 155 microsecond Y delay is combinedwith the 175 microsecond Y-to-X delay, the missing X coordinate can bedetermined by the following equation.

X=−W+(W/H)×Y+{W/[{square root}(H ² +W ²)+H−W]}×V×t

[0542] If the touch is in the zone covered by the X-to-Y sensorsubsystem, then the corresponding equations are as follows.

Y=−H+(H/W)×X+{H/[{square root}(H ² +W ²)+W−H]}×V×t

X=+W+(W/H)×Y−{W/[{square root}(H ² +W ²)+W−H]}×V×t

[0543] The X-to-Y and the Y-to-X sensor subsystems are an example ofsensor subsystems that do not have overlapping touch zones. Thealgorithm in FIG. 25 does not attempt to pair up delay times from suchpairs of sensor subsystems.

[0544] In many cases the redundancy-check algorithm of FIG. 24(a) andthe anti-shadowing algorithm of FIG. 25(a) can be combined. For example,consider the X-Y-U-V sensor of FIG. 14, in which a touch is typicallysensed by four sensor subsystems One coordinate measurement can be lostdue to shadowing, and yet three coordinate measurements will remain tosupport an algorithm requiring a self-consistent triple of delay times.

[0545] The cylindrical sensor of FIG. 19 also provides an applicationfor this type of analysis. As is evident from inspection of FIG. 19(b),any or the following three coordinate pairs, (u,v), (u,φ), and (v,φ), issufficient to determine the (r, φ) coordinates of the touch.

[0546] The spherical cap sensors of FIGS. 21(a) and 21(b) and FIGS.21(c) and 21(d) provide other examples. In these cases, any of the threepossible coordinate pairs (u, v), (u, φ), and (v, φ) is sufficient todetermine the (Θ, φ) coordinates.

[0547] For the sensor of FIGS. 21(a) and 21(b), the anti-shadowingalgorithm is essential to assure two-dimensional touch reconstructionfor the entire touch surface. The v sensor subsystem has a blind regionto between the hole and the transducers R1 and R2; in this region (Θ,φ)coordinates are reconstructed from the (u,φ) sensor subsystem pair.Similarly the u sensor has a blind region between the hole and thetransducers T1 and T1; in this region (Θ,φ) coordinates arereconstructed from the (v,φ) sensor subsystem pair.

[0548] Similarly, the anti-shadowing algorithm of FIG. 25(a) can be usedto optimize touch performance of polygonal sensors such as the hexagonalsensor of FIG. 15(b) and large sensors such as the large rectangularsensor of FIG. 16(a).

[0549] In general, the redundancy-check algorithm of FIG. 24(a) and theanti-shadowing algorithm of FIG. 25(a) allow one to make beneficial useof sensor designs employing redundant coordinate measurements.

Example 20

[0550] If a touch is sensed with more than one acoustic mode, then anadditional characteristic beyond touch position and “Z axis” touchpressure may be determined. Such information may be used, for example,to reject false touches due to water drops on the touch surface.

[0551]FIG. 26 outlines the basic parts of a dual-mode touchcharacteristic rejection algorithm. The first box, delay times fromdifferent sensor subsystems for a touch are associated as a byproduct ofthe touch-position reconstruction algorithms 2601; more generally, thefirst box represents the group of delay times from different sensorsthat correspond to a single touch regardless of whether the touchlocation is actually computed. The second box represents thedetermination of the magnitude of the signal perturbations for the delaytimes associated with the touch 2602; it may be that the magnitudes ofthe signal perturbations have already been calculated as part of a testof perturbation significance. Here it is assumed that not all signalperturbations involve the same acoustic mode in the touch region. In thethird box the signal perturbations are compared with expectedcharacteristics, e.g. ratios of perturbation amplitudes, of validtouches 2603.

[0552]FIG. 26 illustrates the basic features of a dual-mode algorithm.In practice, the dual-mode feature may be incorporated in various waysinto algorithms that reconstruct touch positions, perhaps determinetouch pressure, perhaps provide anti-shadowing and multiple features,etc. The essential feature here is the comparison with expectations ofthe relative magnitudes of coupling of two or more acoustic modes to atouch.

[0553] As an example, consider the sensor shown in FIG. 14 for anembodiment in which the X and Y sensor subsystems sense touches with ahorizontally polarized shear wave (ZOHPS, HOHPS, or Love), and in whichthe U and V sensor subsystems sense touches with an acoustic mode withvertical particle motion at the surface, such as Rayleigh and Lambwaves. To be more specific one may, for example, use a 0.090 inch thicksoda-lime substrate at an operating frequency of 5.53 MHz for which theRayleigh wavelength is 0.0226 inches where the U and V reflector anglesand spacings are given in FIG. 13(b) and FIG. 14 and the X and Yreflector spacings are integer multiples of the Rayleigh wavelength andthe X and Y reflector angles are about 52.5° as needed to coupleRayleigh waves to n=4 HOHPS waves traversing the touch region.

[0554] If such a sensor is subjected simultaneously to a water drop anda finger touch, due to viscosity damping, the finger touch will resultin expected amplitudes of signal perturbations in both the (X, Y) and(U, V) subsystems. However due to the weak coupling of horizontallypolarized shear waves to water, the (X, Y) signal perturbations due tothe water drop will be weak while the (U, V) signal perturbations willbe strong. The weak (X, Y) signal for the water drop will not beinterpreted as a light finger touch because the corresponding (U, V)touch is strong. The ratios of signal perturbations for the same touchthus provides a characteristic of a touch that differentiates betweenwater drops and finger touches. With empirically determined thresholdsfor such ratios, the algorithm can respond to finger touches and yetreject touches from water drops.

[0555] The algorithm of FIG. 26 has other uses besides water rejection.For example, such an algorithm can be used to verify that a user isproperly wearing gloves provided that the type of glove is constructedof a material that has a ratio of radiation-damping to viscosity dampingcharacteristics that is sufficiently distinct from bare finger touches.This feature could be used, for example, to assure compliance withsafety procedures for equipment where the wearing of gloves ismandatory.

Example 21

[0556] A test reflective array is provided having continuously varyingreflector angles, from 45° to 56° with respect to the axis of the array.Other ranges of reflector angles may also be of interest. This arrayserves to produce, at various portions of the substrate, increasingreflector angles that may be experimentally tested for mode-conversionscattering at 90° of an incident Rayleigh wave to a plurality ofpropagation modes. A useful feature of 90° scattering is that thereflector spacing along the axis of the array depends only the inincident mode and not the reflected mode. The reflective array acts as adiffraction grating, directing waves having varying phase velocities atdifferent positions along the arrays.

[0557] It has been found that the optimal chevron angle from the axis ofpropagation of an incident Rayleigh wave for scattering at right angles,for a shear wave of n=0 is about 46°, n=1 is about 47-48°, n=2 is about48°, n=3 is about 50°, n=4 is about 52-53°, and n=5 is about 56°, forglass thickness of 0.085″ to 0.090″, with increasing thickness tendingto smaller angles. The ratio of the phase velocity of a Raleigh wave andan n=4 HOHPS is about 0.92.

Example 22

[0558] The output of a dual-mode algorithm as represented by FIG. 26need not be limited to a simple pass/reject judgment on the nature ofthe touch. The dual-mode algorithm may categorize valid touches amongsta discrete set of categories, or even provide an analog measure of atouch characteristic.

[0559] “Dual-mode” algorithms need not be limited to the use of only twodistinct acoustic modes. Use of three or more acoustic modes is alsowithin the scope of this invention. In this context “distinct acousticmodes” may refer to the same acoustic mode at a significantly differentfrequencies, e.g. Rayleigh waves at 2 and 5 MHz. The essential featureis that not all sensor subsystems couple to a touch in the same way.

[0560] A dual-mode algorithm with a discrete-set output has applicationwith sensor systems used with multiple styli. For example, a set ofstyli may be provided in which each stylus has a tip with a uniqueacoustic coupling properties. The unique acoustic coupling propertiesmay be, for example, a particular ratio of coupling strength toRayleigh-waves via dominant leaky-wave damping mechanism to the couplingstrength horizontal-shear motion via viscous damping. When a user drawson the touch surface with a stylus, the dual-mode algorithm enablesdetermination of the particular stylus used. For example, in anelectronic white-board application, different styli may correspond todifferent colors; depending on whether the electronic white-board iscombined with a display technology, the styli may or might not alsodouble as markers applying, physical (in contrast to “electronic”) inkto the touch surface.

[0561] The dual-mode algorithm may be combined with other techniques tofurther categorize the nature of the touch. For example, the timeduration of the touch perturbation may be used to help distinguishdifferent styli via the size of the contact area between the sensor andthe stylus tip, as is considered in claim 10 of European PatentApplication 9411927.7. The stylus tip may be vibrated at a signaturefrequency, e.g. 100 Hz, in order to modulate the magnitude of the touchperturbation is a fashion that can be recognized by a controlleralgorithm. These and other methods may be combined with the dual-modealgorithm to more reliability or more completely characterize the natureof a touch perturbation.

[0562] Here “stylus” generalizes to anything that results in a touch.For example, consider an acoustic sensor per this invention built intothe bottom of a drip pan. More particular imagine that liquid drops aresensed by both ZOHPS and flexural (lowest-order anti-symmetric Lamb)waves. The ratio of ZOHPS to flexural perturbation magnitudes is largerfor a high viscosity oil drop than a low viscosity gasoline drop.

[0563] As an example of an analog output of a dual-mode algorithm,consider again the above drip-pan application. The ratio of ZOHPS signalperturbation, a measure of viscosity, to the flexural wave perturbation,a measure of leaky-wave attenuation which is weakly dependent onviscosity, is a measure of viscosity. Hence with a dual-mode algorithm,this invention supports viscosity measurement. It is known thatblood-count is strongly correlated with blood viscosity, so a “drip pan”blood-count sensor may provide a portable sensor with fast response inthis case the sensor substrate may be a glass slide and the operatingfrequency may be above 5 MHz to reduce size and increase resolution.

[0564] In a blood drop viscosity measurement system, the reflectivearrays may be formed as a screened frit on the glass slide or as anetched or ground structure. However, where the slide is disposable, thetransducers may be provided separately and as a part of a permanentfixture. Thus, the transducers are pressed tightly against the glassduring testing to couple the acoustic waves, without a permanentadhesive bond.

Example 23

[0565] As shown in FIGS. 32(a)(1) and 32(b)(2), an adaptive thresholddetermination scheme may be implemented with regional variations tooptimize the sensitivity of the touchscreen without causing undueerrors. This adaptive threshold scheme has two slightly differentaspects. First, during initialization, the system rapidly acquiressufficient data to allow perturbation detection. Then, afterinitialization, the threshold is adaptively updated, excluding portionsof the sensor for which significant perturbations are detected.

[0566] Thus, the system initially seeks to determine a baseline input3201, presumably in the absence of touch, for each available subsystem.During initialization, the system may also detect and ignore significanttransient perturbations which may be due, for example, to prematuretouches, and thus the processing scheme for the first and second aspectsof the adaptive baseline processing may be merged. The baselinecharacteristics are stored 3202. It is noted that this baselinecharacteristic data is generally stored separately for each sensorsubsystem of the device. Based on the stored baseline characteristicsfor each sensor subsystem, a statistical analysis of the normalvariations, instability and noise may be made, which may provide a basisfor setting a margin between the normal baseline and a threshold 3203.The threshold may vary based on a signal space of the sensor subsystem,based on the baseline stability in a given region of the sensor or timedelay after transducer excitation 3204. In a normal operational mode,the baseline is determined 3206, without reference to detectedperturbations 3205, and adaptively updated 3207. In addition, thebaseline stability characteristics 3208 and threshold 3209, which mayeach vary based on a position or region of the sensor, and for eachavailable sensor subsystem, are also adaptively updated.

[0567] According to the present invention, a single emitted acousticwave may give rise to a plurality of received signals, representingdifferent transducer subsystems. Therefore, as shown in FIG. 32(b), areceived signal may be analyzed for resolution of information relatingto a plurality of sensor subsystems 3211, 3213, 3215. The system willgenerally sequentially measure the signals from each available sensorsubsystem 3210. However, in some cases, available redundancy may allowthe sensor to operate in the absence of data from one or more sensorsubsystems. Further, at any given point in time, sufficient data may beavailable for certain analyses, even though a complete mapping of thesensor for each subsystem is not complete.

[0568] If the received signal is above the threshold for a givenposition and subsystem 3212, which, for example in a phase sensitivereceiver embodiment, is evaluated 3216 as {squareroot}((ΔI)²+(ΔQ)²)−Threshold (position, subsystem)>0, further analysisensues 3217. Otherwise, no perturbation is deemed detected 3218, and thesystem continues to receive and analyze further data, e.g., from thenext sensor subsystem 3220. On the other hand, if the data from a sensorsubsystem is superthreshold, a significant perturbation is detected, andthis information passed 3219 to higher level, baseline analysis, orother algorithms.

[0569] As shown in FIG. 32(c), after data for some or all availablesensor subsystems is obtained from the perturbation detection algorithm3221, a determination may be made whether sufficient data is availableto proceed with analysis 3222, which may differ for the variousalgorithms. Further analysis of the perturbations according to thepresent invention may then be performed, as appropriate, including ananti-shadow algorithm 3223, a multiple touch/redundancy algorithm 3224,and a consistency algorithm 3225. Normally, the size and shape of aperturbation will also be analyzed 3226, to allow an optimal outputcoordinate to be calculated. If sufficient perturbation data is receivedand analyzed 3227, which as stated above need not include all the data,or data from each sensor subsystem, then a further process ensures thata coordinate representation of the perturbation(s) are normalized into adesired output coordinate space 3228. The actual normalization orcoordinate transformation may be performed at various points in theprocess, and indeed various portions of the process may operate indifferent spatial representations of the perturbation position(s). Thenormalized coordinate representations are then output 3229. Theperturbation analysis is a continuous process, analyzing eachsignificant perturbation. Thus, the processes set forth in FIGS.32(a)(1), 32(a)(2), 32(b) and 32(c) may proceed independently andasynchronously, except where data from one process is required foroperation of the other process.

[0570] The present invention therefore extends the field of acoustictouchscreens by describing such systems which innovate the mechanicalconstruction, receiver electronics and or logical processing systems,for the purpose of providing, among other advantages, increasedflexibility in packaging and configuration, improved performance, andthe ability to process multiple perturbations simultaneously. It shouldbe understood that the preferred embodiments and examples describedherein are for illustrative purposes only and are not to be construed aslimiting the scope of the present invention, which is properlydelineated only in the appended claims.

What is claimed is:
 1. A touch sensor comprising: an acoustic wavetransmissive medium having a surface and a touch sensitive portion ofsaid surface; a transducer system for emitting acoustic energy into saidmedium; and a receiver system for receiving the acoustic energy from thesubstrate as at least two distinct sets of waves, a portion of each ofwhich overlap temporally at said receiver system or overlap physicallyby propagating in said touch sensitive portion along axes which aresubstantially non-orthogonal; said receiver system determining aposition or a waveform perturbing characteristic of a touch on saidtouch sensitive portion.
 2. The touch sensor according to claim 1,wherein said at least two distinct sets of waves from said touchsensitive surface propagate along different sensing axes.
 3. The touchsensor according to claim 1, wherein said at least two distinct sets ofwaves from said touch sensitive surface are of differing wavepropagation modes.
 4. The touch sensor according to claim 1, whereinsaid at least two distinct sets of waves differ in frequency.
 5. Thetouch sensor according to claim 1, wherein said at least two distinctsets of waves are emitted by a common transducer.
 6. The touch sensoraccording to claim 5, wherein said at least two distinct sets of wavesare emitted simultaneously.
 7. The touch sensor according to claim 1,wherein said transducer system comprises at least one array oftransducing elements.
 8. The touch sensor according to claim 1, whereinsaid receiver system comprises at least one array of transducingelements.
 9. The touch sensor according to claim 1, wherein saidtransducer system comprises a single electroacoustic transducer.
 10. Thetouch sensor according to claim 1, wherein said receiver systemcomprises a single electroacoustic transducer.
 11. The touch sensoraccording to claim 1, wherein at least two distinct wave paths intersectat a non-perpendicular angle.
 12. The touch sensor according to claim 1,further comprising a reflective array, situated along a path, said pathnot being a linear segment parallel to a coordinate axis of a substratein a Cartesian space, a segment parallel to an axial axis orperpendicular to a radial axis of a substrate in a cylindrical space,nor parallel and adjacent to a side of a rectangular region of a smallsolid angle section of a sphere;
 13. The touch sensor according to claim1, wherein said at least two distinct wave paths share a common segmentwherein substantially all of the wave energy of each wave path travel.14. The touch sensor according to claim 1, wherein said at least twodistinct wave paths do not share a common segment wherein substantiallyall of the wave energy of each wave path travel.
 15. The touch sensoraccording to claim 1, further comprising a reflective array intersectingacoustic paths, having a two dimensional Fourier transform with at leastone useful spacing vector component.
 16. The touch sensor according toclaim 1, further comprising at least two reflective arrays intersectingacoustic paths, each having a two dimensional Fourier transform with oneuseful spacing vector component.
 17. The touch sensor according to claim1, further comprising a superposed reflective array intersectingacoustic paths, having a two dimensional Fourier transform with at leasttwo useful spacing vector components.
 18. The touch sensor according toclaim 1, wherein said transducer system comprises a superimposed array.19. The touch sensor according to claim 18, wherein said superimposedarray has a two dimensional Fourier transform with at least two usefulspacing vector components for waves scattered at differing angles. 20.The touch sensor according to claim 18, wherein said superimposed arrayhas a two dimensional Fourier transform with at least two useful spacingvector components for waves of differing frequencies.
 21. The touchsensor according to claim 18, wherein said superimposed array has a twodimensional Fourier transform with at least two useful spacing vectorcomponents for waves of differing propagation modes.
 22. The touchsensor according to claim 1, wherein said receiver system comprises asuperimposed array.
 23. The touch sensor according to claim 22, whereinsaid superimposed array has a two dimensional Fourier transform with atleast two useful spacing vector components for waves scattered atdiffering angles.
 24. The touch sensor according to claim 22, whereinsaid superimposed array has a two dimensional Fourier transform with atleast two useful spacing vector components for waves of differingfrequencies.
 25. The touch sensor according to claim 22, wherein saidsuperimposed array has a two dimensional Fourier transform with at leasttwo useful spacing vector components for waves of differing propagationmodes.
 26. The touch sensor according to claim 1, wherein said at leasttwo distinct sets of waves intersect at angles between about 10 and 80degrees.
 27. The touch sensor according to claim 1, wherein said atleast two distinct sets of waves include a Rayleigh wave and ahorizontally polarized shear wave.
 28. The touch sensor according toclaim 1, wherein said at least two distinct sets of waves include ahigher order horizontally polarized shear wave.
 29. The touch sensoraccording to claim 1, further comprising a reflective boundary forreflecting sets of acoustic waves.
 30. The touch sensor according toclaim 1, wherein said at least two distinct sets of waves comprise atleast three distinct sets of waves.
 31. The touch sensor according toclaim 1, wherein said at least two distinct sets of waves have differingaxes of propagation, said receiver system comprising at least twotransducers, each receiving a portion of said at least two waves. 32.The touch sensor according to claim 1, wherein said at least twodistinct sets of waves have differing axes of propagation, saidtransducer system comprising at least two transducers, each emitting aportion of said at least two sets of waves.
 33. The touch sensoraccording to claim 1, wherein said at least two distinct sets of wavespropagate simultaneously in said touch sensitive region.
 34. The touchsensor according to claim 1, wherein said at least two distinct sets ofwaves do not propagate simultaneously in said touch sensitive region.35. The touch sensor according to claim 1, wherein said receiver systemis sensitive to waveform information of said received signals.
 36. Thetouch sensor according to claim 1, wherein said receiver system is phasesensitive to said received signals.
 37. The touch sensor according toclaim 1, wherein portions of said at least two distinct sets of wavesshare are incident on a single receiving transducer simultaneously. 38.The touch sensor according to claim 1, further comprising means fordetermining the characteristic of the touch based on a pattern ofperturbation of the received signal corresponding to a superposed waveconsisting of portions of each of said at least two distinct sets ofwaves.
 39. The touch sensor according to claim 1, further comprisingmeans for recognizing perturbations in components of said receivedsignal derived from each of said at least two distinct sets of waves.40. The touch sensor according to claim 1, wherein said surface isplanar.
 41. The touch sensor according to claim 1, wherein said surfaceis cylindrical.
 42. The touch sensor according to claim 1, wherein saidsurface is a large solid angle spheric section.
 43. The touch sensoraccording to claim 1, wherein said at least two distinct sets of wavestravel over differing paths, said receiver system determining a positionof a perturbing influence and producing an output including a coordinateposition, at least one of said coordinates of said coordinate positionbeing calculated based on a transform of signals representing at leastone of said sets of waves.
 44. A touch sensor comprising: an acousticwave transmissive medium having a surface and a touch sensitive portionof said surface; a transducer system for emitting acoustic energy intosaid substrate; and a receiver system for receiving acoustic energy fromsaid substrate, said receiver system analyzing a perturbation of saidreceived acoustic energy in waveform sensitive manner.
 45. The touchsensor according to claim 44, further comprising a filter forselectively analyzing received acoustic energy signals corresponding toacoustic energy traveling a predetermined path from said transducersystem.
 46. The touch sensor according to claim 44, wherein saidreceiver system analyzes a phase pattern of said acoustic energy fromsaid substrate for determining a position or a characteristic of a touchon said touch sensitive portion.
 47. A touch sensor comprising: anacoustic wave transmissive medium having a surface, an edge, and a touchsensitive portion of said surface medial to said edge; a transducersystem for emitting acoustic energy onto said touch sensitive portion aswaves traveling along a plurality of sets of paths; a receiver systemfor receiving acoustic energy from said touch sensitive portion fromsaid plurality of sets of paths, said plurality of sets of paths havingat least two components propagating along a path intersecting arespective position along said edge, differing in propagation angle withrespect to said edge.
 48. The touch sensor according to claim 47,further comprising means for determining a position or a waveformperturbing characteristic of a touch on said touch sensitive portionbased on at least two of said plurality of sets of paths.
 49. A touchsensor comprising: an acoustic wave transmissive medium having a surfaceand a touch sensitive portion of said surface; a transducer system foremitting acoustic energy into said medium; and a receiver system forreceiving the acoustic energy from the substrate as at least threedistinct sets of waves which propagate in the touch sensitive portion;said receiver determining a position or a waveform perturbingcharacteristic of a touch on said touch sensitive portion based on saidat least three sets of waves.
 50. A control for determining a positionof a touch on a surface by means of sets of acoustic waves havingincrementally varying paths, portions of at least two of said sets ofwaves being received simultaneously at an electroacoustic transducer,comprising a phase sensitive circuit, retaining phase information ofsaid portions of at least two of said sets of waves.
 51. A control fordetermining a position of a touch on a surface by means of sets ofacoustic waves having incrementally varying paths, portions of at leasttwo of said sets of waves being perturbed by a touch, comprising atransform processor for producing an output representative of a positionalong a single axis based on information derived from each of said setsof waves.
 52. A control for determining a position of a touch on asurface by means of sets of acoustic waves having incrementally varyingpaths, portions of at least two of said sets of waves being perturbed bya touch, comprising a processor for determining a positional consistencyof information derived from each of said sets of waves.
 53. A controlfor determining a position of a touch on a surface by means of sets ofacoustic waves having incrementally varying paths, at least two of saidsets of waves differing in frequency or wave propagation mode,comprising a processor for determining a characteristic of a touch basedon said sets of waves.
 50. A control for determining a position of atouch on a surface by means of a set of acoustic waves havingincrementally varying paths, receiving signals corresponding to said setof acoustic waves, said control being capable of sensing a perturbinginfluence by detecting an increase in a signal amplitude.
 51. Asubstrate for an acoustic touch sensor system comprising: anacoustically transmissive medium having a surface with a touch sensitiveregion having at least one side; at least two reflective arrays,disposed parallel to one another and on the same side of the touchsensitive region, together having a two dimensional Fourier transformwith at least two useful spacing vector components.
 52. The substrateaccording to claim 51, wherein said two useful spacing vector componentsare for waves scattering at different angles
 53. The substrate accordingto claim 51, wherein said two useful spacing vector components are forwaves of differing frequencies.
 54. The substrate according to claim 51,wherein said two useful spacing vector components include at least oneacoustic wave mode conversion.
 55. The substrate according to claim 51,wherein said reflective arrays are superposed.
 56. The substrateaccording to claim 51, wherein said reflective arrays are not coaxial.57. The substrate according to claim 51, wherein said reflective arrayseach comprise reflective elements, corresponding elements of eachreflective array having differing angles.
 58. A touch sensor comprising:an acoustic wave transmissive medium having a surface and a touchsensitive portion of said surface; a transducer system for emittingacoustic energy into said medium; and a receiver system for receivingthe acoustic energy from the substrate, for determining a perturbationof said acoustic energy due to a touch on said surface, said touchsensor comprising a reflective array having a plurality of spacedelements for scattering portions of an incident acoustic wave as waveshaving a different propagation vector than said incident wave andpassing other portions unscattered, said array being provided an arrayselected from the group consisting of: (a) an array associated with saidmedium situated along a path, said path not being a linear segmentparallel to a coordinate axis of a substrate in a Cartesian space, asegment parallel to an axial axis or perpendicular to a radial axis of asubstrate in a cylindrical space, nor parallel and adjacent to a side ofa rectangular legion of a small solid angle section of a sphere; (b) anarray situated along a path substantially not corresponding to a desiredcoordinate axis of a touch position output signal; (c) an array situatedalong a path substantially non-parallel to an edge of said medium; (d)an array having a spacing of elements in said array which differs, overat least one portion thereof, from an integral multiple of a wavelengthof an incident acoustic wave; (e) an array having elements in said arraywhich are non-parallel; (f) an array having an angle of acceptance ofacoustic waves which varies over regions of said array; (g) an arraywhich coherently scatters at least two distinguishable acoustic waveswhich are received by said receiving system; and (h) combinations andsubcombinations of the above, except that said array in (d), (e) or (f)is not provided parallel and adjacent to a side of a rectangular regionof a small solid angle section of a sphere.
 59. The touch sensoraccording to claim 58, wherein said array is associated with said mediumbeing situated along a path, said path not being a linear segmentparallel to a coordinate axis of a substrate in a Cartesian space, asegment parallel to an axial axis or perpendicular to a radial axis of asubstrate in a Cylindrical space, and parallel and adjacent to a side ofa rectangular region of a small solid angle section of a sphere.
 60. Thetouch sensor according to claim 58, wherein said array is situated alonga path substantially not corresponding to a desired coordinate axis of atouch position output signal.
 61. The touch sensor according to claim58, wherein said array is situated along a path substantiallynon-parallel to an edge of said medium.
 62. The touch sensor accordingto claim 58, wherein said array has a spacing of elements in said arraywhich differs, over at least one portion thereof, from an integralmultiple of a wavelength of an incident acoustic wave, said array notbeing provided parallel and adjacent to a side of a rectangular regionof a small solid angle section of a sphere.
 63. The touch sensoraccording to claim 58, wherein said array has elements in said arraywhich are non-parallel, said array not being provided parallel andadjacent to a side of a rectangular region of a small solid anglesection of a sphere.
 64. The touch sensor according to claim 58, whereinsaid array has an angle of acceptance of acoustic waves which variesover regions of said array, said array not being provided parallel andadjacent to a side of a rectangular region of a small solid anglesection of a sphere.
 65. The touch sensor according to claim 58, whereinsaid array coherently scatters at least two distinguishable acousticwaves which are received by said receiving system.